Given the gathering following of the various WSM combinations (as in folks will use a 7mm bullet in all 3 of the WSM cases - 7, 270, and 300) in competition, I think they are safe inthe long run. I would be a bit mroe concerned with the SAUM, as its be discontinued in virtually all manufacturers. Too bad as in most conditions it will run with the WSM on velocity and uses less powerder to do it. Good article here on the various 7mm cartridges (.284, .284 improved, SAUM, WSM). Rumor has it from th eLapua booth at SHOT this past January that Lapua has 300 WSM
brass in the queue for maybe 2012 or 2013. Lots of folks take the 300 WSM brass and neck it down to 7mm.
7mm Cartridge Guide within AccurateShooter.com
If you go SAUM (I personally think its a hell of a round), I would buy brass in bulk now and store it for future use to overcome the only possible hardship - finding brass a couple of years down the road.