The point would be to reduce initial load times, yes?
Principally I like the idea, although I'm skeptical about the loading triggered via a user interaction - because that would bring the waiting back. It'd probably be nicer to load it at the beginning, too, but not wait for that plugin to complete to move on with the rest of the loading process. Thing is, the plugin would've have to declare whether it's "lazy-loadable" or not itself (e.g. batchpages would probably never want to be loaded lazily). Which triggers the issue that the containing SWF would have to be loaded anyway, which is the bulk of the waiting time, normally...
As an alternative you could try using the - or a customized - fat client. That gets rid of some redundant code in the plugins, thus saving quite a bit in size.
