I'm sure when DDR4 comes out, 16-24GB of ram would probably be a midrange to budget system. There's always a use ... if anything, Windows 9 is going to use 16GB just by itself "just because it can". Games will take at least 8GB because we love our 8K by 8K textures on our next gen 4K screens. Having 1TB in servers would probably be typical for interactive, dynamic VR applications and processing.
This is assuming we still use DRAM... holographic memory anyone?
Never underestimate innovation if you give it time.