This is not the best idea in my opinion, and let me explain why.I agree there, I know that a lot of people tend to troll as it is in their bios. Plus if it was unlimited people could keep adding onto it everyday and every time something happens to one of their characters. Personally I wouldn't want to read a really long bio, longer yes that would be perfectly fine, unlimited would be stretching it a bit.
The chance for spam bios would increase and they could just have never-ending bios that go down forever, and not to mention sometimes it's nicer to have much shorter, concise bios. We don't always need to know what your character's breath smells like in the morning, or about that one time they went for a stroll in the park.
Although a much larger space for bios would be nice, unlimited would be pushing it, and I don't think the game could handle that for long.