Some of the things you bring up are interesting.
In the games that I've played / read the "arc" seems to shift around this level for a very similar reason to the one you've given, the "next" group of story related bad guys being too tough for the PC's to handle.
The paths I've played / read through seem to shift the arc to another location in an effort to "find" something or "check out" something that may or may not directly tie into the overall plot at first glance.
Personally I really like this. It allows for a change of pace or even an entire different feel. Somewhere along the lines the PCs do end up seeing how the adventure fits in and why it's very important... It may take a while longer, but it happens.
What is very common in the 9-12 range is an event, discovery, whatever that changes the PCs from being almost entirely reactive to almost entirely proactive. This can happen for many, many different reasons.
Whatever you decide to do definitely make it cool. Levels 7-11 are where the game is best.
Have fun.