[spc476]

Not really. The TMS9900 [1] used memory as registers and had a fairly compact instruction set. Yes, it does have registers, but only three (a program counter, a status register, and a pointer to the current "register set" in memory). At the time, it was regarded as a slow machine, probably because of all the memory-to-memory operations.

[1] https://en.wikipedia.org/wiki/Texas_Instruments_TMS9900

[throwaway000002]

Sure, this is one technique. You could also, akin to jump instructions, have a concept of data locality, versus instruction locality. You can do this is a lot of ways without resorting to something like segmentation, which everybody hates. Trivial would be something like a current "data pointer", which would see useful implicit updates, and well as explicit ones (akin to a long jump).