I don't think Mental Misstep will get the hammer. The main reason is that WotC doesn't really give a shit about Combo decks, and their beloved aggro and aggro/control archtypes were really improved by MMS.
Still, the card was really format warping, and every single deck is trying to either run it, or play arround it (like we did, with those new techs).
BUT, if I'm wrong, T.E.S and ANT will make a huge comeback, because Innstrad gave them a new bomb: Past in Flames. And, as 4eak said, we'll have to speed up.
So I'd try the good old LED lists with FKZ + Sphinx. I've been testing it lately, and I've found the 8 Leyline sideboard build pretty strong. Something like this:
Lands [12]
4 Cephalid Coliseum
4 City of Brass
4 Gemstone Mine
Dredgers [12]
4 Golgari Grave-Troll
4 Golgari Thug
4 Stinkweed Imp
Draw [9]
4 Breakthrough
3 Street Wraith
2 Deep Analysis
Business [14]
4 Lion's Eye Diamond
4 Cabal Therapy
4 Bridge from Below
2 Dread Return
Creatures [13]
4 Narcomoeba
4 Putrid Imp
3 Ichorid
1 Flame-kin Zealot
1 Sphinx of Lost Truths
Sideboard [15]
4 Leyline of the Void
4 Leyline of Sanctity
4 Chain of Vapor
1 Ichorid
1 Iona, Shield of Emeria
1 Elesh Norn, Grand Cenobite
Well, LED lists have only 12 lands, and only 8 can produce Green mana, so you can't rely on Ancient Grudge/Nature's Claim/Ray of Revelation with consistency. So the way to go is Leyline of Sanctity, which is a real catchall (prevents Bojuka Bog, Crypt, Relic tap, Ravenous Trap, Nihil Spellbomb).
Leyline of the Void is mainly to keep your bridges safe, but has several other uses. And at last, Chain of Vapor, which can be cast off Cephalid Coliseum.
It was pretty good testing, although LED is a little inconsistent. Turn 1 kills happened, Turn 2 kills were common and Turn 3 kills were mandatory.
Any thoughts?