Having Ral keep stuff tapped on opponent's turn would be crazy broken. He'd be better cheaper Tamiyo at that point.
As it is the untap part of his ability is probably way more useful, since Sorcery speed tapping isn't particularly great. I do like the choice it sets up with creatures where you can either give one of your guys pseudo-vigilance or make it so an enemy creature can't block, but not both.
You can do both. The great part is he's good against opposing control decks as well since he forces opponents to keep extra mana up each turn, and can accelerate you in an Izzet deck.
I hope I can get my hands on some copies, since I really want to build an Izzet deck (or an Izzet-Simic collaboration).
Split cards look like they might be taking up lots of card slots, since they'd have to make a ten-card cycle of both the uncommon and rare ones. Still, I've always loved split cards, and Fuse looks like an even more interesting way to do them.
On unrelated news, I didn't know Second Sunrise and the cards in it were so expensive. I have all the cards back from before Extended changed and Modern was added (ie: no Faith's Reward or newer goodies), but I don't think I'll be playing that deck at all since it bores me to no end... should I go and trade some of the cards away?