You mean like an extension cable so you can put the ram somewhere else?
If so, no. Memory is switched at a very fast frequency and the distances have to be very exact. Timing has to be perfect for memory to be refreshed. (Memory timing is measured in billionths of a second as a comparison, even back in the day)
Unlike PCIe which is serial communication. Errors can be re-transmitted. With memory, errors will likely lead to a crash. (Which is why Error Checking and Correcting memory is a thing, and slower than non-ecc memory.)
A product typically exists if it serves a purpose. Any riser cable for a DIMM would need to use the DIMM slot to begin with... If the DIMM slot was limited in such a way (cooler clearance, perhaps?), then there are low-profile options available to work around that.
I believe there was a line of Macs still used a daughterboard for memory in the last decade or so, but that's not a "riser" that would match your description.
I think there would be a market for it if it could be made to work. (Overclocking would probably be out of the question)
With RGB being so popular people want to show off everything and with many air coolers you don't get to see much of RGB memory, particularly when you want all the slots filled. Which leads to a lot of water coolers with RGB fans so they can be seen.
I'm surprised there isn't a line of SO-DIMM RGB memory and a board that prominently displays them. Could turn the face of the PCB into an elecroluminescent panel. Though most people using SO-DIMMs are doing small form factor where the memory wouldn't typically be visible anyway. Or full size DIMMs in a SO-DIMM like slot so they are splayed out at an angle. (That would probably take a lot or re-tooling)
Such does not exist for the reason/s already stated. The longer pathways required would introduce a multitude of timing issues. Yes, 4 and 8 slot SIMM to DIMM cards did exist in the old days, but, memory timings were much much looser back then as well. Today every fraction of a millimeter matters.