I wouldn't mind seeing the older actors, but maybe not as the Doctor. Here's a 30-second idea:
1. Weird time-fragmenting thing happens with the TARDIS
2. Somehow leads to the Doctor's incarnations getting Arched and living out their lives. Logically, it shouldn't be possible, but the TARDIS got hit with a dose of timey-whimey. Maybe 4's a professor emeritus at Oxford? That way, it makes some sense that they look way different from their last appearance.
3. 11 has to TECH the TECH to reset the timeline, and he has a brief encounter with each incarnation, who don't know that he's them.
Just a thought. I'd like to see something, but I'd probably prefer it not be within the context of a regular story.
I think that this is a pretty cool idea. I suspect, however, that for the 50th anniversary most fans would want to see each of the Doctors featured to appear as the "genuine article", so to speak- rather than alternate versions. I really do like your idea, though, and wish that we could see such a story with one or more other such alternate Doctors leading alternate existences.