I'll reassign this to me, as I'm looking into making Program Files the default location for 3.5.

I'd like to release at least some of the alphas with the change active by default (i.e. it's easy to select the old directory) to get broader feedback. So far I haven't encountered any trouble other than in pip (as is being discussed at https://github.com/pypa/pip/issues/1668).

If things don't work well in the early releases of 3.5 we can easily revert the change, though I suspect the main feedback is going to be about the amount of typing required. In that case, I'll look into hardening the permissions on the root directory as part of installation.

Unless some really bad scenarios arise, getting the legacy permissions will be opt-in. As 3.5 will be the first version with that change there shouldn't be any direct back-compat issues - we can't make a change like that in maintenance releases or even 3.4.