Yes, that does sound like a polaris/ktm thing. Initially I heard that they were going to come out with a 400cc sport atv (Like the Artic Cat DVX I suppose) then later I heard it was a 520. I saw the 510 as speculation on another board. Just a rumor though. I have heard many. Some pan out, some don't.
I sure hope this one is happens though! I would like to see a 4 valve larger displacement sport/racer atv. In the US we don't take the 250 ATV class serious.