[verall]

SRAMs are catching up, but they are still much less dense, and are normally configured for smaller line sizes and lower latencies than DRAM. DRAM requires sense amplifiers and capacitors which have scaled both scaled slower than transistors.

From a systems perspective, lots of work has gone into hiding DRAM's faults highlighting its strong points, so a system where DRAM is replaced with SRAM will be more expensive but not realize most of the possible benefits without major redesigns of the memory systems.

Intel has some xeons with over 70MB of L3 and also released some eDRAM chips to play around with this idea, but notice they used eDRAM to get 128MB of L4 on a consumer chip - SRAM is still very expensive!