Sorry for any confusion with support tweets. Everyone is on the same page now. According to the recent blog posts, Mojang would like to keep capes as Mojang-given only. I know it's a bit unusual for the company to moderate which kind of content is allowed in mods, but I've confirmed with some higher-ups that this is their wish.
if this mod can't give out capes, then optifine can't either. you still get an optifine cape for donating.