Since 1.8 you're able to harvest the red and brown ones with silk touch, but the others two and currently unavailable. I think it'll be nice to have them for decoration.

Closing all further suggestions as of now. Since quark is a mod for features that will go in vanilla, post your suggestions to /r/minecraftsuggestions and tag me (/u/vazkii) if you want me to see it. I take notes of all features I intend on adding.