Ok, sorry for the huge post, but when you asked for features, I ran away, started writing, and couldn't stop.
vim specific feature requests:
1) I 2nd drisner's request to be able to visually select then : to go to a command prompt that applies to the selection only.
This should apply to commandmode actions on said selection as well. Block mode selections should also be able to make use of this idea. When I use <ctrl>v to select a block of text, I should be able to perform any commandmode action on that selection. Eg. cw to change a visual block to some new content across the whole block or > to shift the block to the right, a '/' search should extend the selection to the next match. etc.
2) Block cursor while in command mode, 'I' cursor while in insert mode.
3) Register handling: while in command mode "*y with something selected copies (y for yank) selection to the '*' register. "*p pastes. Vim registers can do MUCH more, but this is all I use since I can't use <ctrl>c <ctrl>v.
4) Vim macros. I know vslick has it's own macro language, but...
I use the macro recording functionality in Vim regularly to do extremely simple tasks repeatedly. I haven't learned slick-c, so I can't comment on how the functionality compares. I'll go do that. It's still a request... While in command mode qm records my next keystrokes (both commandmode and/or insertmode) to macro m, until I hit q again. @m repeats macro m. 100m repeats macro m 100 times.
5) Work out NDA (or whatever) to actually work with Bram Moolenaar and incorporate the real vim into VSlick... Ok, I can wish, right?
vslick generic feature requests:
1) Don't undo every cursor movement, only undo edits/actions or offer a setting in preferences on undo behavior.
2) Undo should only undo 1 action at a time. If I perform a > (vim for shift right) twice, each > is a single undoable action. Ditto with '.' to perform last action again. Each action is one undo step and should only be un[re]done one step at a time.
3) Make smart next window smarter, ie. <ctrl><tab>. It gets lost sometimes and brings up buffers I haven't accessed recently prior to ones I have. Possibly fixed in a later rev. I'm on rev 9 and just beginning my v11 evaluation period.
4) Install in "C:\Program Files\" by default on windows platforms instead of C:\.
5) On windows, default VSLICKCONFIG to "C:\Documents and Settings\USERNAME\Application Data" instead of My Documents or $HOME. I set this specifically, in my environment, a long time ago. I'm not sure if it applies anymore.