Is there by any chance a way to dynamically set the clock frequency oder enable some kind of power saving mode on the Carambola?
I was thinking about using the Carambola for a portable battery powered design, where full processing power is only needed on external events (such as user interaction or incoming network traffic). But the Carambola's power consumption is a bit too high for a long lasting battery powered application (at least in its standard operating mode).

Do you have any board based on these or plan to make any?

I have a TP Link 703N, a AR9331 chip. It's a very capable chip and runs cool. We were considering it before the carambola. Only think we can't use it that it has limited GPIO exposed. Perhaps you guys should consider using the AR9331 instead.

I wolud really appreciate a ar9331 module because of the awesome low power consumption.
Would be a good project for imho ...

So what would it take to design/produce an AR9331 based board? Lack of I2C is not a problem because there is an openwrt module that does I2C over GPIO using just 2 GPIO. 1 serial is enough.

The TP Link 703N would serve as a great reference. Just need to expose the other GPIO.