What the poll at 
<a href="http://igor2.repo.hu/cgi-bin/menu-poll.cgi"> http://igor2.repo.hu/cgi-bin/menu-poll.cgi </a>
suggested (at the moment of closing it in 2017 October):

<b>[multikey2]</b> The default menu file should offer two sets of hotkeys:
<p>
<ul>
	<li> multikey hotkeys (e.g. "f s" for "file, save" or "e c" for "edit, copy", similar to how it is done in gschem)
	<li> single key hotkey, that always has a modifier if it is a [a..z] (e.g. ctrl+s for save, ctrl+c for copy).
</ul>
<p>
This would allow the transition to multi-key (pretty much unaviodable if
we want to add new functions with hotkeys) and still keep single-key items.
(Multiple hotkeys for the same menu item should work.)
<p>
However, we wouldn't be able to keep single key alpha hotkeys, such as
'o' and 'f' - they will have a multi-key variant and probably a
single-key-with-modifier variant (and in return some other
single-key-with-modifier of our less often used hotkeys will lose their
single-key-with-modifier to make room for these)
<p>
<b>The <a href="../menu2">new menu file is ready</a> and we have switched over to it</b>