Brainstorm can't be compared to Mental Misstep because you have to splash a color to play Brainstorm.
Also, Mental Misstep + Snapcaster would be way too nutty; keep in mind the mana cost has an alternative cost so you can still pay 2 life or U.
Cards I want to see come off in the near future, in no particular order and not all at the same time:
Mind Twist - Rarely going to be better than Hymn to Tourach. The only card that might potentially break this is Dream Salvage and somehow I doubt it. By the time its better than Hymn to Tourach, your opponent in most cases will be sitting on a number of cards that would make it basically an overcosted Hymn or slightly better than Hymn.
Survival of the Fittest - This card was fun to play with and against... til Vengevine. I'd say switch the two on the banned list.
Earthcraft - It might get played but it won't wreck anything.
Black Vise - Its about time we had a solid, easily splash able hate card for blue decks. Reanimator might be a lulz inevitability turn 2 so WotC will print a splashable 1cc hate card (Cage) as well as Dredge, but blue has solidified a permanent position in the DTB. It would likely be good against slow control decks but Tempo decks can comfortably sit out of range at 4 cards.
Mind's Desire - Discussed to death, but safe. Worse than Time Spiral in High Tide combo and wouldn't even get played along side it as Meditate is better is more situations, while Ad Nauseam is a better engine for Dark Ritual combo. At most TES would get a new Wishboard toy but we'd have to consult Mr. Cook on that.
Frantic Search - This one doesn't get nearly enough attention in the B/R threads. It got unbanned in Vintage, perhaps its safe for Legacy as well. It would make Solidarity an actual deck again, which would be nice considering Spiral Tide got, well, an engine. Spiral Tide would also play it but Solidarity would probably be better as the deck wouldn't have to run Candelabra's, and run into Pithing Needles, QPM, etc. while its setting up. You can't really Snapcast Frantic Search unless you're already sitting on 5 lands, so I don't think Tempo would play this, especially since its a cantrip that gets easily Pierced/Dazed. Ponder is way better in Tempo. Frantic Search would likely be played in Reanimator, Dream Halls, SnT.
Worldgorger Dragon - Reanimator is already stupid enough but its GG if you resolve a creature like Iona, Jizzlebrand anyway. You hate it with the same cards either way and we've acquired much better post-board hate for Reanimator since Dragon was legal.
Not so sure:
Oath of Druids - May I refer people who want to protest this choice to Show and Tell which for 3 mana basically does the same thing. Would having both in the same format suck? Perhaps but an enchantment can be dealt with via QPM/GSZ before he has mana to activate it, unlike SnT. I'd like to hear thoughts on this one.