2.5 for a six cylinder is really on the small side of displacement. These days you find more often that there are 4 cylinders up to that displacement, it's sort of that threshold where one can either make a big 4 or a small 6 (Mazda3s now have 2.5 fours, used to be a 2.3). I don't see anything wrong with using the same displacement with two fewer cylinders and some forced induction...so long as it sounds right.
I'm sure that for right now they're going to stick with what's there and wait until the last possible minute to introduce new style engines to meet regulations. Too much money has been invested in the engines already out there and improving upon them in what's coming up on 15 years. Since things always sort of trickle down from flagship cars, I figure the same will happen for the Boxster unless they decide to pull a little from VW here, a little from Audi there, which I'm sure is very likely for anything that's not a 911. The only thing I'm hoping they don't do is try to put an inline TSI engine from a GTI in the car and still call it a Boxster.
