Will they show blood? Maybe they will, maybe they won't. Can they show blood? Absolutely. Remember Disney's Tarzan? It had a "G" rating, and included this scene, among others.
I'm not saying that they have to, or even that they ever will. I'm just saying that anyone who says "they can't show blood" is wrong.
Kids get little scars and cuts from falling down when they're out playing all the time, it'd make sense for their favorite characters to get themselves a little beat up from time to time as well. We just don't particularly need to see it. Whenever there's a fight or implied injury, you see bandages, that's far enough.
MLP seems to be fine with fake blood, possibly the same for small bits of blood that imply death. Question is, just what the hell is likely to happen that would require bleeding ponies?
There will never be blood in this show, it's a children's cartoon for pete's sake this is not Family Guy or American Dad it's My Little Pony I repeat MY LITTLE PONY.