Wimax won't change anything. The problem with "muni wifi" is not the technology, it's the business model. If Tempe AZ had Wimax today, it still would not have kept the model from failing.
http://wifinetnews.com/archives/007869.html
The real benefactors of Wimax will be the cell phone companies. Whereas Wifi uses unlicensed spectrum (Part 15), the majority of Wimax will utilize licensed spectrum at higher power.