For point 4, there's no code in either the 3.5 or the 3.4 (AFAIK) installer that would remove a py.ini file. From 3.5 onwards the py(w).exe files will be properly refcounted so the latest version is always installed regardless of order (i.e. 3.6 will update 3.5's but 3.5 won't downgrade 3.6). It isn't possible to make this backwards compatible with 3.4 at this stage, though we *might* be able to make it backwards compatible with 3.4.4.

I think I'm the only one who's made changes to launcher.c recently (apart from Paul Moore's patch, which I reviewed and applied). Not that I want to be nominated as a maintainer for it :)

"py.exe -h" never seems that useful to me, but that's mainly because the help from python.exe takes up a full screen and hides the rest. I'm not sure that providing the ini paths here would help, since that doesn't tell you what you can set, but having a link to the docs would be fine.

I have no problems at all with adding more details to the docs. When I refreshed the rest of that page I didn't really touch the launcher section IIRC.