Re: BuddyPress and Shared Hosting
Your analysis in the paragraph above outlines exactly what users can expect or aim to acheive with shared hosting. The fact that it can be installed and operated is one thing, providing a desirable user experience is another.
The restrictions on shared hosting though may allow for a WPMU installation but not provide enough flexibility for some BuddyPress plugins to work, but as you say too many variables to be discussed here.
If BuddyPress does end up supporting single-user wordpress I’m sure that the net will undoubtedly widen.