yea memory compression will probably occur sometime soon (I wonder how much lag it gives you though).
ALSO, there are many experimental memory types (magnetic RAM etc) under developement by many companies.. far too many to track for me.
after compression, I would think that some sort of move to serial will HAVE to occur. I mean, sortof like RAMBUS, but not implimented in their way (I'm sure you can achieve high mhz without having to use the exact same method as them).