First off, what an awesome platform you guys are developing! I’m a die-hard Excel fan, and even use Excel Online. But this is posing to be a real threat to that.
I have a suggestion for a field type that I, and probably others, would find useful. Sometimes I like to use little icons (but not checkmarks) as data in fields. Kind of like tags, but image-based. Multi select or single select choices would be cool too.
As far as the icons themselves, you could start with some basic ones: a star, exclamation mark, up/down arrows, basic emoticons. And you could allow users to create/upload their own.