Although Live started out as a DJ/dance application (mostly), film composers are starting to want to use it, too. But as brilliant as Live is, it cannot be taken seriously for film work without mixed meter. Period.
Ableton, since there aren't as many film guys as there are DJ/dance guys, you probably won't get tons of requests for this feature. Most of your user base probably doesn't need it. But if you want the film community to take you seriously, you've got to add mixed meter.
It's not enough to have Live slave to dp or Logic via ReWire. Matching the tempo isn't enough; the *bar numbers* must also match.
PLEASE. PLEASE. PLEASE.