Thanks so much jonradio! This is (almost :P our dream come true! I'm working on a group blog which wants to be like an online newspaper with various sections and a "front page" with a survey of everything. We tried WP Multisite, which works pretty well, but as a "fake webmaster" (non-developer / non-coder) I wasn't able to find a way to get the "Front Page" (primary site of the multisite) to auto-display posts from all the child-sites.
Since the child sites all used the same theme anyway, we decided Multisite might not really be necessary and it did require adding authors over and over, making menus over and over, etc. So jonradio Multiple Themes became a way for us to use a main theme (currently WooThemes Scrollider) and then add in another theme, WooThemes Teamster for our author pages / author archives.
It's almost brilliant! Unfortunately the "trick" you document using Theme Test Drive to setup the alt-theme isn't quite working for menus (nice to have) and number of authors to show (essential for us) I won't go on about that here, I'll go post in the forum.
Even though this small problem if unsolvable might unfortunately wind up having us not use jonradio Multiple Themes, I still wanted to give it 5 stars as it's a marvelous plugin if you can make it work. Maybe this "switching" is too specific or too fancy for WordPress Core, but I'd think that a lot of users / designers would want this ability. I guess you could hack a theme into a custom post type, but again, as a "fake webmaster" IDK what's even involved in that.
Thanks also for the extensive documentation, screenshots, etc. For a fairly unusual functionality, it's pretty easy to set up. The multiple switching passes: jonradio:deactivate, theme-test-drive:activate, work on site, reverse, repeat... does get a little tedious, but once you had a site setup, you shouldn't have to go through all that again soon.
Thank you so much!