If at all possible, have the international kit end at the same time as the base set, or preferably before it. That way you won't lose people who really need the international to tip, as the base is useless without it for some people, me included. For this drop the cyrillic only set is a nice fallback though.
As for the cyrillic set, could you add the ISO/cyrillic keys to it? (R3 "/\" and R4 "\|" or also "/\", depending on source. I'm not Russian so I would not know for sure). As we all know, soviets used the ISO layout (or at least it was used by many systems), so it would be nice to include the keys to allow that option.
Edit: on a closer inspection I get more and more confused about the layouts in various cyrillic keyboards. Still an ISO option would need just 2 more keys to the kit. One ISO layout to cover could be the Ukrainian ISO cyrillic, which would need maybe just one additional key on top.