Cute, but I can do the exact same thing in Vim. It has built-in commands :Pick, :Reword etc that change the current line, and I've just defined my own ftplugin/gitrebase.vim file that looks like:
nnoremap <buffer> <silent> <LocalLeader>p :Pick<CR>
nnoremap <buffer> <silent> <LocalLeader>s :Squash<CR>
nnoremap <buffer> <silent> <LocalLeader>e :Edit<CR>
nnoremap <buffer> <silent> <LocalLeader>r :Reword<CR>
nnoremap <buffer> <silent> <LocalLeader>f :Fixup<CR>
nnoremap <buffer> <silent> <LocalLeader>c :Cycle<CR>
This way I just press e.g. "\p" or "\f" (my localleader is \) to change the line, which makes it just one more keypress than your command, but I have the full power of Vim and I don't have to go about changing my editor.