What cards would you like Downshifted?
Personally i think the Tri lands from Shards of Alara like: Arcane Sanctum etc. Would be interesting, as they would provide an on more flexible manabase for splashing a third colour or even making 4-5CC possible as well.
I also think that Fear of Isolation the skyfisher from duskmourn that triggers on cast instead of ETB: would also be a nice addition as it would possible open up for a Jeskai or Izzet Synth lines.
When on this line of thought for Izzet anyways, how about Expressive Iteration? Doesn't seem busted but would give a nice 2 for 1 for 2 mana, that i think the blue decks as missing currently.
I could honestly also see Goblin Lackey in the format as the biggest thing you can put into play would be Skoma, which yes is a 4/4 but doesn't do a whole lot if there wasn't a creature down to block the lackey already.
I also think Spectral Procession would be a very nice addition for the mono white decks and it might even open up some go wide token stragegies that we don't really see in the game currently outside of Kuldotha.
other considerations on my part.
thirst for Knowlegde.
Lightning Helix.
Kitchen Finks.
Harmonize.
Vendicate.
Putrify.
Mortify.
Trygon Predator.
Rhox War Monk.