I agree that a constructed league with the same card pool from week to week would be nice. It would probably need to be a shorter league (2-3 weeks instead of 5) so that people didn't get bored.
That said, an interesting league could be:
Series 1: Sets 1-3
Series 2: Sets 4-6
Series 3: Sets 7,8,10
Series 4: Sets 1-10 (or something ... I'm less confident on this one)
Also, I think each series should be 1 week long, not 9 days. It would be easy to remember something like Collectors change on Mondays, Sealed on Wednesdays, and Constructed on Fridays, unlike the current version where there's no easy way of remembering when each series is going to start.