Who's going to be buying all that HBM? I don't have anything that I can drop it into and I haven't heard of any consumer products coming soon that will use it.
OpenAI will be the key, as they have a huge inventory of DDR5 (both finished and unfinished modules) and thus will have a lot to dump at some point once they finally convert their servers over to HBM. Altman was at one point even intentionally depleting retail memory supplies by sending employees and contractors out to retail stores in an attempt to buy out everything they could get their hands on to limit competitors.
Beyond that, though, you are right about the HBM.
It might or might not be useful for producing GPUs (which AMD has done in the past, with the R9 and Radeon VII lines), but I don't see any motherboard manufacturers --- presuming there are actually any left by that point --- producing consumer products that could use it.
The domestic Chinese market might be an exception, as they have made an art and industry out of scavenging existing technology to make things that weren't designed (or intended) to work together to do so.