One of the problems with having a lot of hybrid cards is that it makes it difficult to give the color combo it's own identity, especially since he's only running three gold card per guild. I think it's important for the colors to have payoff cards that you can expect to wheel if nobody else is playing those colors. If your Selesnya section has three cards, and two of them are Finks (staple) and Militant (not really a staple), there's only one other Selesnya card in the entire draft that's a "payoff" for being in that combination. I think that's a very real downside of going heavy hybrid. In general, I avoid hybrid except in cases where the card is a staple (Finks, Redcap, and to a lesser extent, Cackler) and/or the quality is so high that I can't cut it. I have five cards per guild (405 cards in the cube), so I feel like I'm isolated from this effect and it doesn't bother me so much.
I suppose if you went all-hybrid, that would make for an interesting take on it though.
I would agree about the supplemental printings. That would give you access to Baleful Strix, Brago, Shardless Agent, Song of the Dryads, etc. I'm sure there are more I'm not thinking of right now.