I would miss caps lock. As soon as I see >2 upper-case letters in a row, I use it. I don't know how people bother to type long acronyms and other words in caps without it.

> I'm not sure it would be such a good idea to implement a hodgepodge of random peoples' mappings.

Ctrl-C is not a (user-defined) mapping. It will leave insert mode, but will not trigger things like abbreviations and autocommands (in Vim), so it's not a good idea to use it over Ctrl-[ (which is supported) or <esc>.