Fascinating - I think corn as a food source would be awesome. So many different possibilities of different products can come from that. o.o
Glad to see this back. I loved your 1.8 posts. I'm feeling so psyched about that path block. I can see a lot of cool uses for that, and I love the look of it. It's kind of like a mixture of hay blocks and dirt.
For the boss bars? There will probably be a limit on how many the client will accept. I don't assume that there will be a setting for it though.
Optifine will probably have a setting for it. It seems like one of those things that would lag the client.
I don't see it being too much of a problem to the client at all. All the server does is tell the client to create the bar (with extra details sometimes such as percentage filled etc.) the rest is done client side.