I didnt think it was on the Corvette chassis. If it is on it now, then they'd better keep the next gen on it. If it handles like a Corvette, it should definately stay on its' platform to keep its handling edge.
It is indeed on the C6 platform. The XLR is built along side the Corvette in Bowling Green, Kentucky. The XLR has been something of a disappointment to Cadillac, sales wise. But because it is built where it is, and with a very popular and profitable sister vehicle, it will probably continue. It's handling and performance seem always to be praised. It's magnetic suspension system is also well regarded. In my opinion, the interior holds it back. As well as the pricing. It should sticker for about 10% less than it does.
Mercury is alive and well. It's called Lincoln.