Neat build!

I'm not saying it NEEDS a revamp, but if you want to toy around with it:

Have you thought about splashing Black into this deck? That could help a lot with your control vs. creatures (particularly in Legacy format).

Vampire Hexmage is pretty much the other staple combo card with Dark Depths. You might also toss another Thespian's Stage in there as well just to complete that combo set for "speed Depths" too either way.

Slow Motion can be evil recurring control for you, I've got a midrange deck that uses those to devastating effect. It can be fun to stack them up on a creature the opponent is hell-bent on saving, only to lose out and return them all to your hand for a repeat.

Propaganda is another card I use in my blue control deck and it's quite effective (especially with multiples in play).

Index can be quite helpful in a deck relying on combos for speed. 1 mana for Scry 5 can be brutal and give you a massive advantage off the draw.