I ran into one of these companies, in 2015? at a big data conference. The founders claimed to have not known about iram, ;) It feels like PIM comes up every couple years, but ram is expensive already, and these chips are going to be some multiple more expensive. There is some inflection point ,memory bandwidth, power, something that will enable PIM to finally get traction.
The immediate problem was tooling, os support, supply, scale, etc. I think it would make a lot of sense to get this stuff installed sitewide after your code has been tuned for support. So it needs a good simulator or it needs an interposer so one can code to the ABI of the hardware.
I could see a big super computer initiative being used a test bed, probably one designed for genomics. I think we overestimate how effective and easy to use PIM (processing in ram) could be. Where it will really start to shine is when the processor can retire instructions into the PIM, pre-materialize data streams from the PIM, do a scheduled reduction and then push compute bundles back to memory. The computational ram needs to be integrated with cpu, it can't just be an accelerator.
Computational disks might be way way easier to implement. We will know how that is going as soon as Western Digital tells us.
But how does this differ to a CPU or GPU? Both are just DRAM with something bolted onto the side, and both have a limited bandwidth between the DRAM and the processors. The difference with putting the processors on the DIMMs is that you now have an extremely restrictive thermal envelope to work within (and if you put it on the same die, which I hope you're not, then a CMOS technology that's supremely ill suited to computation).
Here is an existing implementation: https://www.upmem.com/