A release which is likely to be an entirely new game rather than an expansion as we've seen with TBD/HoW/TTK.
Okay, if we're going down this line, then I will bite.
This is entirely my own opinion, it has no basis in fact, but it makes logical sense.
You don't need to re-write an engine (the engine being the thing that handles network code for P2P/Dedicated Servers/etc) to drop consoles. Rockstar did it with GTAV, new patches introduce content for New Gen only, and Bungie can do the same thing ... will they? We don't know.
I see numbered sequels more as new engines, and to implement a new engine means old "assets" will need to be redesigned, and re-engineered ... that is, all the worlds (Tower, Cosmodrome, Moon, Venus, Mars, Dreadnaughts, etc) and all the Crucible maps as well. It could be just a case that Bungie already has high poly versions of these assets they will export to the new game, they may also already have high resolution textures ready to go, but that doesn't discount the fact there will be an absolutely massive amount of work involved to do this, we're talking multiple years of development by a large team.
Then, and only then, do I believe Bungie will consider dedicated servers, because the engine redesign will permit such a large scale change.
But the real question is, will they?
That's where I believe the answer is No.
For one, I believe the Destiny Engine (whatever it's called internally) will evolve, it won't ever be re-written. Over the span of 5 years it may as well have been re-written, but it won't be a major team effort spanning multiple years of coding.
Let's think of how long between releases for new games, Fallout, GTA, etc ... each time there's a new game, it takes multiple years with absolutely NO content in between, could you play Destiny in its current form for 2 years? No, neither could I.
This is why I believe the game will evolve with smaller dribbles of content more regularly as the engine and content evolves and Bungie tweak and fix things underneath, it helps keep the players engaged, it also allows them to improve the back ends.
I have nothing to back any of this up more than "It makes sense if you think about it".