I think POWER is infeasible because of TDP. The 4-core typically draws around 60-92 Watts. I have a dual 8-core sitting next to me for AI research, and my experience of getting it working is a terrible pain because you have to flash the firmware, and the procedure for the initial flash is…tedious. Raptor has good intentions but it is not ready for the regular (even privacy conscious) user. This is a hurdle any one will need to overcome to make a mass-market product.
IBM’s decision to ditch Thinkpad was a good business decision. They were haemorrhaging money. The product they made was more costly than the market would allow. Try as they did, they just couldn’t get people to justify buying a $5,000US laptop for regular business use so they sold at a loss and tried to slowly increase the prices. As they did so, market share dropped. Lenovo recognized the reputation of ThinkPad, bought the brand, and restructured their entire company around that reputation (which they subsequently destroyed, imo).
I cannot think of a single product that IBM just stopped supporting in the last twenty years without obsoleting the product. That said, I don’t know the entire portfolio. However, even after Apple ditched POWER, IBM kept selling and supporting that same line of processors. Since most of their direct costumers are nation-states and security savvy mega-corps, the firmware on the POWER8 and beyond is open. Also, IBM has stated it doesn’t want to get in the legal gray area of providing backdoors for any purpose–that’s up to the firmware supplier (which, honestly, is still usually IBM).
As for RISC-V, I think given a few years it’s feasible. They know they have some performance issues and they are actively working on that. My understanding is there is a variant of Ubuntu that is being used for testing.
I recently saw a start-up trialling a laptop with 4 8-core Cortex-A75, and a 4-core A53. The A53 handled bootstrapping and shutting down the other four processors, and minor tasks. The machine had some whacky firmware issues (eg with all 4 A75’s up, only 7 cores could be used on each, attempts at virtualization caused a kernel panic), but typical battery life for the person testing it was 16-18 hours typical, and the performance I observed was quite good. The use in question was browsing, typing articles and technical documents, video calls, and watching movies on a plane with Wi-Fi off. I saw it used to play ported versions of a couple of popular gaming titles from a few years ago (that I cannot name) with ease. I have no knowledge of what graphics chipset it used that I’d assume some Mali variant.