Well, all platforms change every few years, the only difference being Slot 1, which has marvelously had a very long life - you can still use old LX based motherboards, and throw in a Socket 370 CPU onto a slocket, if the bios supports the CPU, and get quite good performance out of an ancient platform.
AMD has claimed that they are committed to Socket A. It makes sense for AMD to stay with Socket A as long as possible, as motherboard manufactures, historically, have been more amiable to changing their designs for Intel boards than AMD boards (due to sheer volume). I'd say you should have at least a year left for SocketA, if you're lucky, maybe a little more.
EDIT - I made a typo - had to replace "Slot A" with "Slot 1"....my bad