We are also looking at something similar. Have you looked in the the new getOffer(s) function in at.js2.x? It's possible to deliver multiple regional mboxes in one call. However, our initial tests show a significant performance impact when compared to 1.x. Not sure the cause of the performance impac...

Agree. There are examples out there on doing this with profile script based on mbox name but that's not really relevant because frequency capping is usually done based on the content or offer not the mbox.