The Dark Eyes boxsets in retrospect i.m.o served to prove he wasn't a man who would be able to sacrifice even a few innocents lives for the needs of the many, or willingly walk down the road to double genocide, and how given the choice, he'd always strive for peace if deep down, he still had hope things could change, as he says to the Master, 'I will not join you in this insane war across the timelines!'. There's a difference between character development and outright character rewriting, as such I would have found t pretty hard to buy him as the War Doctor role as Moffat envisioned it-the War Doctor was set up and hyped as a massive contrast to 10 and 11, and even though he ended up being a red herring of sorts and more of a regretful old man, I think breaking 8 down into a warrior, only to have the climax of the storyline (Gallifrey being destroyed) being averted would have rendered much of the development pretty pointless, at least the War Doctor adds more mystery to the conflict and gives writers complete freedom to write for a very different sort of Doctor.

Although Dark Eyes does reinforce the idea of McGann becoming darker, to me the 8th Doctor's darker aspects have always been more of a reaction to the writers experimenting with and testing his impulsive nature and high moral idealism, rather than any natural inward darkness. Even in his lowest moments, his arc in the audios was more concerned with testing his Doctor, then pulling him back from his snapping point, rather than breaking him completely i.m.o.

Of course there's no way of knowing how much the more recent boxsets were rewritten in the wake of Night Of The Doctor, but assuming at the time Big Finish wanted to stretch the gap between Dark Eyes and The Time War as wide as possible (as they have confirmed ‘it’s a very long way to Karn…’), they could be fighting a losing battle with listeners, who would naturally want to hear the time war as soon as possible, but once you break the doctor there's no going back, knowing that no matter what the 8th Doctor would end up as a burnt out but brutal warrior, would i.m.o derail his gradual character arc and limit how far Big Finish could take the character, before things became very depressing, cyclical and repetitive, at the time there was no guarantee their license would have been expanded to New Who, with Hurt's Doc now appearing in audios, I think the buildup to the time war won't be as rushed as it could have been, and there will be a more believable evolution/contrast of the doctors attitudes during the time war, Hurt's Doctor opens many more doors than it closed i.m.o.

But assuming McGann been cast as The War Doctor, Big Finish had stated many times before they are keen to stretch the lifespan of The Eighth Doctor as much as possible, using McGann as The Doctor who fought in the war for centuries could have pigeonholed how far they could experiment with the character i.m.o, at the time of the 50th Anniversary, they had no idea if their license would be renewed or extended to cover New Who properties, and there's no guarantee McGann (or listeners) would have been happy exploring such a different version of his Doctor. With the 8th Doctor in particular there's a much stronger case for following his story chronologically, and things would only get cyclical and stale if you were always fighting the temptation to show the build up to the war or show a Doctor Gone Dark, it's hard to believe a 'time war' would have started overnight or linearly i.m.o, now BF have a largely outcast 'War Doctor' to write for, they can keep some of the time war mysterious, and can still tell the 8th Doctor's involvement in great detail, 8 and War operate very differently as Doctors, so there's room for a wider variety of Time War era stories i.m.o.

For many I think one of the attractions of using McGann as the War Doctor was the idea of his untapped potential, and the arc of a 'lover' being forced to become a fighter, which is a fair enough point of view, and certainly a interesting arc from a dramatic angle. For a doctor that started out questioning himself 'WHO AM I!' and expressed such a clear love of the universe, having his final actions lead to genocide and the destruction of his homeworld would have a tragically ironic ending, and given McGann some amazing material to work with as his soul was crushed by the weight of an endless war. However it's clear in DOTD that The War Doctor wasn't quite the boogeyman he was hyped up to be, and as one of Moffat's points with DOTD was to prove, no matter how dark the circumstances, he was at heart still the Doctor, much of the tragedy of having 8 as the war doctor would have been lost i.m.o (though of course you could argue the 'happy ending' would have counterbalanced this'). Therefore, I think Moffat (who judging by the way he wrote him, has a clearly defined interpretation of the 8th Doctor's character) would have been even less inclined to make the 8th Doctor as dark as some fans wanted, for me it would be a little too metatextual and a bit of a slap in the face to use the 8th Doctor in the timewar, his doctor doesn't need 'redeeming' as such i.m.o, and without the destruction of Gallifrey remaining permanent there would be little meaning or finality to such an arc (whereas the War Doctor started out as warrior, so saving Gallifrey was the opposite sort of climax ashe was redeemed rather than outcast).

Other problems I had in turning McGann into the War Doctor are simply pragmatic, as we see in Day Of The Doctor it’s the final day of the War, all the implied rage and fire of the War Doctors early years (given that he's been regenerated especially to fight by the Sisterhood, I'm guessing he'd have more fire and rage than an already rather old and worn down 8th doctor could have when the time war breaks out) was long gone in Moffat's script, casual audiences wouldn't have any idea as to how McGann's romantic scatterbrained adventurer had become this broken and battle hardened, it’s hardly fair to go and say to them 'Go and listen to several decades of audios, which are years away from catching up to this point anyway to get the implied context, by the way due to the BBC charter we can't really refer to the audios directly in the show anyway' to get them caught up with the Doctor's change in temperament. McGann's Doctor was so full of life and energy, it's very hard for me personally to picture him so cold and broken...

Personally I don't think it's an arc that is really backed up with McGann's work in the audios, I'd have felt very cheated not seeing such a change in the flesh, and I don't find it as fulfilling or interesting from a dramatic point of view, it just seems predictable the happy guy going dark and sad, The 8th Doctor has already been pushed to the brink with so much heartbreak, tipping him even further over the edge just seemed a bit...cynical. And having become a fan of the BBC 8th Doctors novels (which will hopefully be adapted by Big Finish one day...) McGann being the time war Doctor sits somewhat uneasily with me...what are the chances the same Doctor who though 'pushing the button' (albeit a very spur of the moment decision) deliberately didn't destroy Gallifrey permanently, to stop a war from starting, would contemplate destroying it completely after deliberately fighting in an even bigger war voluntarily for centuries?, it would be both retreading and cancelling out old ground for the 8th Doctor...of course you could argue if he'd already done something similar before, what's to stop him doing the same thing again...I suppose it all depends on how idealistic you think the Doctor should be written...

Having come to know the 8th Doctor I'd have found it a massive kick in the teeth if they broke down McGann's heroic wanderer into a blood soaked outcast completely devoid of hope, only to have the destruction of Gallifrey reversed anyway, it would have probably redeemed McGann's Doctor in the eyes of many fans, and given him time to shine on screen but i.m.o it would have drastically altered his character for very little gain.

I'm personally of the opinion that some wanted McGann as the War Doctor because they didn't really know his Doctor and wanted to see more of the mystery explored, not because it was supported by the source material or his Doctor’s character. Now thanks to Moffat's gamble, we have two doctors in the war-one a Doctor trying his utmost not to become a warrior, only to be pushed by circumstance into becoming one, and a warrior gradually becoming a doctor again, it's a fascinating duality with huge potential and with the forthcoming Time War Audios for each Doctor presumably running in parallel there's going to be some very interesting comparisons to explore...