I would be very surprised if they did... 6.5mm don't have much of a folling in the US, therefore they don't sell well.
Remington came out with the 260 a few years back, and due to what ever reason they pretty much never pushed the sales on them... I think they were to worried about getting their Short action UM out. I the only thing that the WSM would have over a 264 is the lenght of the action. There isn't much of a market for the 264 so I don't think Winchester will waste any time developing one to put into production. If you really want one I would suggest rebarreling a rifle for the cartrige.
Wildcater's have been shooting this round since the 300WSM came out. I think there are two different versoins. One being based on the 300 and the other on the 270. I don't remember which one has a longer OAL. but the longer one would create higher velocity thus making it a little more desierable. RCBS has dies for it so it would only take a little playing to get the dog barking.
Ivan