This is really what will drive the show's format: What will draw viewers and boost ratings.
I found it to be about as exciting as watching paint dry on on growing grass.
"Reunion" shows have generally been successful ratings-wise, but I know of only one (Survivor S8) "Reality-Show" that had an All-Star season. It was a ratings juggernaut too, so I can see the TPTB of DWTS wanting to tap into that possibility. It is a more complex format though, since DWTS has always focused so strongly on the couples.
That might be a reason to start out an All-Star season with teams of rotating Pros/Stars competing - much as auntie thesis suggests. It might be a way to initially break some of the old couple-y ties while still retaining the relationships and camaraderie. New ties and rivalries would develop over a few weeks that would build a bridge to a new "Reality" and a new set of couples. Maybe even have people vote for favorite pairings after seeing them all dancing together for a couple of weeks. Some clandestine meetings and maneuvers could also help spice up the season's start.
I say all this with some remorse, as I too have my favorite couples that I would love to see dance together again, and many of the Pros have become favorites over time. But I realize not everyone has the same favorites, which is one of the reasons that the show reaches such a wide audience. (See #1 Goal above.) However, I think it would be possible to create new favorite pairings, using old friends and rivals, that might be just as fun to watch.