Counter Balance, Counter Spell, Daze, Force of Will, Spellstutter Sprite, they are all very commonly played cards in legacy that have been gettin all up in your stack, messing with your spells for as long as I can remember (you might be able to remember a time befor this but I sure as hell don't).

So what I am suggesting is that Summoning Trap might be viable in legacy, not because its ability to cheat fatties into play, we have cards that do that for half the price, but because it is instant speed and can potentially come down for free.

With the ability to manipulate the top of your deck I'm thinking that Summoning trap can take up as little as 5 slots in the deck.
Summoning Trap dodges counter balance (you could even run a creature into the balance for a free trap)

Dropping emrakul at instant speed helps to avoid things like CAB Jace or board sweep.

Lim-Dul's Vault would probably be a wise choice to play, being able to put emrakul or friend ontop of you're deck at instant speed.

I think the core of the deck would be something like:

3 Lim-Dul's Vault
4 Brianstorm
4 Summoning Trap
4 Force of Will

1 Emrakul
4 Tarmo
4 Nimble Mongoose