Support for R (replace mode) would be lovely. I keep trying to do this from vi/vim muscle memory and getting tripped up when it doesn't work. I know that c* or mouse selection is a workaround, but not nearly as fast for making many changes.
Has been a wishlist item since 2011 at http://help.vicoapp.com/bugs/r-for-replace-overwrite-mode-does-not-work-r2207