I have two issues with the idea of the sims team putting together a tween life stage.
1. As @Daephene has pointed out, is it worth the time? This would no doubt be an enormous coding lift, that would take programmers away from other things for an extended period of time. And that's just to make sure that they can do activities that children and/or teens can do, as appropriate. Novel game play would be a whole additional megillah. I would much rather they focus on new game play for the existing life stages, some of which are a bit neglected.
2. It takes kids so long to age up to young adults as it is. An additional youth life stage would mean that unplayed townies might not even survive to see their kids reach high school, which would make me sad. :'( If I wanted an orphan crisis in my saves, I would download Dickensian CC and create workhouses for the poor waifs.
