Rated 3 out of 5 stars
The idea is very good, but so far "interactive themes" from thunderthemes.com are installed with restart like normal themes and not on the fly, while that's the greatest advantage of using "lightweight" themes.
Also, lack of the basic instructions, e.g. whether Personas extension is required or should be disabled. It's not obvious.
You are correct, right now thunder themes provides XPIs.
This page - http://brandthunder.com/personas/getmore/ - provides themes that can be installed with one click.