I'll buy anything released for DCS, but a tanker would be a waste of resources that could be spent on "fun" planes.
I've been working the KC-135 for the last 4 years and I've flown on a few AR missions. While it's awesome seeing another plane that close in flight and the view from the boom pod is pretty amazing, the whole flight profile isn't terribly exciting. Basically standard IFR flight and at some point another plane flies up and the boomer sticks the nozzle in the other jet, then they go away and then it's back to a regular IFR flight and landing. :)
Don't get me wrong, it's fun to watch & experience, but there's not a whole lot more to it than flying any IFR flight in FSX aside from the CRM and specific AR procedures. The boom doesn't do a whole lot, it looks a lot tougher to be a receiver. However, I'm a huge fan of anything DCS and I'd buy it, I just think there are other heavy aircraft with a lot more exciting missions, even a slick C-130.