Jim, certainly this is a good idea, but probably it's really always come down to the expensiveness (and the exhaustion in setting up) of the demonstration workshops.
But a "Demonstration Workshop III" or "Beyond the PIRA 200 Workshop" certainly has been an idea I've heard floated around before, and perhaps when the meeting is going to be in a location where high attendance is expected, and located on a campus where such a workshop could be conducted without causing equipment conflicts for Demo I & II, it could really work out. As I recall a discussion in Greensboro, that equipment issue is one of the harder ones to work out. But as future meeting locations become known, perhaps such a harmonic convergence could work out!
The Committee on Apparatus now no longer has to consume 2 of its assigned sessions on Demo I & II since AAPT has institutionalized them... (or the organizers have been institutionalized

) so a Demo III at least has a better chance to be sponsored by Ap-Com.
I take this as a sign you'd volunteer to be one of the organizers of a half-day workshop proposal for a first try at an Advanced Lecture Demonstration Workshop?

I'd be glad to help organize when the right time comes along. I think something analogous to the Advanced Laboratory Workshop would work for an afternoon session.
For what it's worth, about a dozen years ago, there also used to be a regular workshop on Operation and Organization of Lecture-Demonstration Facilities.... perhaps the Advanced Lecture Demo Workshop could be a fusion of that operational/management side with Beyond the 200.