Based on feedback I've seen so far, it seems like the best short-term fixes will be along the line:
- modify texvc to provide baseline information to fix PNG positioning
- this should reduce the worst problems with PNG math fitting poorly with inline text
- disable the old partial HTML & MathML modes
- keep the 'Leave as TeX' mode to be used with existing user scripts for MathJax
with medium- and long-term:
- give blahtex another look (PNG and proper MathML output to replace texvc?)
- see about cleaner integration of MathJax, with automatic fallback to PNG
- track down a few more bugs with MathJax rendering before making it default
Anything else that should modify those priorities?