Are installation and associated troubleshooting questions on-topic for this site, or do we want to focus on questions/answers that improve users' actual usage of vi(m) and related software?
Installation is very OS-specific. Questions about dpkg, apt, rpm, etc. will probably get better answers on Unix & Linux. Similarly, questions about weird Windows installer errors will get better answers on Super User. Those aren't really vi/vim questions, those are really questions about those other programs. So those really shouldn't be here.
However, questions like picking which features to include in vim (or which package to download, based on those features) are mainly about vim, and that would seem appropriate to ask here. Similarly, many questions about installing vim plugins. The same applies, of course, to other vi-inspired editors.
In short: If the question is really about the package manager or installer, and its just incidental that the package involved is vi/vim/etc., ask elsewhere. Otherwise, feel free to ask here.
Yes, they should be on-topic. We want this to be one place for all Vi/Vim-related questions and answers. Let's use an installation tag for such questions.