I think a lot of features -- especially if you want them accessible inside INSERT mode -- are accessible through CTRL+letter, no? At least omni-completion, the most useful one, used to be when I last tried it. (Has that changed? I'm not doing much editing in vim these days, so I may be wrong.)
Any command that I can think of can be mapped to work while in insertion mode.
The key however is understanding that if you are insertion mode, then key sequences start with the escape key, or, insertion commands are completed with the escape key. There is no "context switching". No more-so then having to press ctrl along with the rest of your key sequence in Emacs is "context switching".
