Consult is very good. But as someone who played combo with consult beofre it was restricted, I can tell you it's a card with real drawbacks. It's obviously great, but it's not DT. DT is perfectly reliable.
Consulting for a restricted card or a 'one of' loses you the game a lot of the time. Not just from the risk of having it in your top six (very real), but from how many cards you may need to remove before you reach the 'one of'. You can remove all your win conditions. You can remove all the swamps and strand a fetch land. You can remove too much draw and have no velocity. Sometimes it's just the bottom card in your deck. The great consult decks of the past were built around 4 ofs (4 necro 4 ritual 4 illusions 4 donate), or were built around wishes (consult for burning sac led in response). The later is much weaker now that wishes can't bring a card back from excile anymore and that the wishes are themselves restricted.
Consult wouldn't just plug into storm and be DT 2-5, it would need to be in a 4of style deck. Something like the below:
#Draft 2 card monte with consult
Draw / search (10)
2 defense grid
2 red blast
4 ancient tomb
7 sol lo mox
4 gemstone mine
4 city of brass
I think that would probably be a strong deck; one that put up top 8s and occasionally won large events. But I don't think it would dominate the meta and win everything. Some new decks get added and life is good.
Of course, maybe consult just goes into PO storm and the deck makes space for 4 maindeck tendrils kills people on turn one all the time and life is awful.
If people want to add power to combo, consult probably adds more power than flash. Flash makes one new deck, consult creates a whole new deck building challenge of finding the best 4of based combo in vintage (hope that combo is not just 4mentor+deck).
Just to note the epistemic status of these posts, I'm mostly trying to brainstorm and engage in outside the box thinking about unrestriction and not tunnel on one card. I don't really have any firm confidence in the belief that consult would be a good unrestriction and would need a lot of deck building, goldfishing, and live testing to get to a point where I could say anything with even moderate certainty. I'm just trying to keep people thinking here and to keep people questioning assumptions about what could be unrestricted.