It's not the power level of the cards that are unbanned, but rather the speed of being able to put a 4/4 with a Clique rider on it while not having to spend your first turn playing a mana dork (nor having to build for mana dorks either).

If the list you mentioned were unbanned, you would see this:

• Ancestral allows for card draw in blue decks. T1 Ancestral, hold off THE MENACE until your turn 4, and then you draw 4 cards. Doable? Yes. Reasonable? Well, your T4 play better be either some way to stabilize or you lose. Hope you are playing UWx for board wipes, hopefully Supreme Verdict.
• Bloodbraid Elf follows a similar line. It's not reasonable until T4, and then you either get a kill spell, discard spell (ick) or another creature (hopefully Goyf). The 2-for-1 aspect is powerful, but if you never get to cast it you can't get the card advantage. A 3/2 in a world of 2/Xs and X/4+s also doesn't exactly do well, so you might have a difficult time utilizing BBE for anything other than a free 1-3 mana spell which may simply do nothing.
• Stoneforge actually seems reasonable. T2 Stoneforge -> T3 Batterskull allows you to tangle with most of the Eldrazi favorably for a bit while you build towards another creature and 5 mana. Once that hits, you are able to suit up something like a Clique, Flickerwisp, something, and start beating down in the air while simultaneously being able to block them profitably for a while. Eldrazi rarely gains life (can they?), so a Germ is a 5 turn clock, SFM + Batterskull is a 4 turn, Flickerwisp + Skull is 3, and anything with 6+ Power is a 2 turn clock. Considering that you need to hold them off with Batterskull to start, it's not a losing proposition, but probably not a winning one either.
• Jace is too damn slow. Sorry. The card draw is bonkers if you get to resolve him, but he comes down with 3 Loyalty, and then goes up to 4 do that he doesn't die to Bolt or something, right? Yeah, Eldrazi has probably flooded the board by now. If you wait a turn and go Wrath --> Jace, then you might have a chance considering their haster is Eldrazi Obligator, but you are still looking at a bad situation if they steal your only blocker with Obligator. If you can protect him the card draw is invaluable, but you're more than likely not going to see him survive 2+ turns.
• DRS is a good-ish option to fight Eldrazi... sort of. He was banned because of T1 Ramp early and T20XX inevitability with spells, which is cool. He can block the Scions, so that's nice, but then on top of that he can proceed to clear out of the graveyard for some much-needed lifegain. It all comes back to the general problem though -- how do you deal with 4/4s on T2, how do you deal with 3 2/Xs on T1? DRS can give you the lifegain and the ramp to hit the spells you need (T1 Fetch, Breeding Pool, T2 White Source, T3 land Wrath?), but you are still dealing with an aggressive deck that is difficult to beat in a lot of scenarios.

There are obvious changes in the way the decks play, but looking into the future is hard. Adding new cards to try to counteract powerful cards is difficult if there isn't raw power on targeted answers. The reason Affinity was never like 1000% of the meta was that it had reasonable hate. Burn is constrained by it's draws. Zoo can slow down or speed up depending on a bunch of factors, but you still, in the end, end up with a deck that can be hated out by something like an Anger of the Gods. Eldrazi isn't slow, nor is it tiny, which is the power of this deck. It also has disruption, and doesn't need any sort of support cards (like Tokens's anthems) to be fast or big. It doesn't rely on mana dorks either. This is a deck that because of it's nature is basically an aggro deck with creatures as big as if not bigger than Midrange decks. Because of Modern as a format, 4 mana Board Wipes are probably going to come back into popularity because of this mess. The only other way to slow them down is Bridge/Propaganda effects, but I digress.