I've read a bit about compressed object pointers in some 64 bits Java VM implementations. As I understood it, the principle is storing a reference as a relative 32 bits address offset from one object to another instead of a full 64 bits pointer, to gain memory.
I believe that this kind of optimization is not currently applied to the .NET CLR. At least I couldn't find anything about it. Could it be potentially applied to it or would that be an impossible/useless/performance-degrading optimization because of how the CLR internally works?
Though I'm not sure if you can do such a thing in .NET, a 64 bit machine generally has an abundant amount of memory (generally 4 or 8G), so saving a few 4 bytes won't have much effect. I would class it as "not very useful".
A quick Google hasn't shown me any signs of .NET being able to support (or even any interest in pointer compression/ORA).