The last version was released in February 2011 and it does not support the latest features in OpenGL. Does anyone know when we can expect the next version to be released? Should I move on to GLSL instead?

Well, the next Cg toolkit will probably be released sooner or later (on official website, the last version in 3 from Feb 2011). Although I strongly recommend you to move to GLSL.

Why? Well it is quite simple, Cg support is good on NVidia gpus, although it suck a lot on AMD ones; On the other hand GLSL support is "same good" (there are differences, though small ones) on both.