I had heard the original plan (from last summer) was to shoot both sequels at the same time to save money - just like the two sequesl to The Matrix. That plan was scrapped when the costs soared, again just like The Matrix.
The rumor is now that instead of two all-star, big budget sequels the next one will use the same planned script and cast - but will now also "set-up" a new, lower priced, cast for #3 and beyond. There's also whisper of someone trying to put together a TV series, but I think that would be well, well beyond ABC's ability to spend at this point.