A bitmap for fonts is pretty simple, but unfortunately just making lookup table from the UTF-8 space doesn't do some languages justice. Many of those characters are actually modifiers that modify other characters, and don't print anything at all; also, some languages (e.g. Arabic) work best if you can support ligatures.
Also, I was thinking something with a bit more depth and weight to it than a simple bitmap.
True, it could; but there's nothing stopping NQ from adding more fonts in the future. There would also be nothing, at least as far as I can tell, that would keep an industrious user from making their own with voxels. I'm thinking more for those folks who just want to save a bit of time and headache from having do it that way.
Ideally (to both points), it would be nice if there was a way of typing out letters in voxels with whatever font you wanted. But dealing with fonts outside of bitmaps with simple kerning rules can be a bit of a nightmare.