Most consumer mobo's I see support this even if the setup isn't on the QVL. If a DDR5 motherboard support 4 sticks at all you can probably run 192gb on it so long as you update the BIOS firmware. The problem is running at rated speeds.
AMD tends to be worse than Intel, and I hear people having to run anywhere between DDR5-3200 to DDR5-5200. You are better off running two sticks, because even with 2 sticks you really can't run larger models with acceptable performance anyways, much less with 4.
There is competition to apple on the low end (dual channel fast DDR5) and on the high end (8+ channel like Xeon/Epyc/AmpereOne). In the middle, Apple is sort of crushing because if you run a true 4 channel system you're going to get poor performance if you load up a 192gb model, and if you compare pricing to 96gb/128gb apple systems, there's not all that much of a cost advantage and you have to make a lot of sacrifices to get there. The truth is that Apple really doesn't have all that much competition right now and won't for the foreseeable future.
I don't think it's realistic to pin your hopes on Qualcomm given that they're unlikely to care about supporting anything other than LPDDR with their laptop processors.
I’m optimistic about APUs personally like AMDs upcoming Strix Halo APU with a 256-bit memory bus competing at the lower end of the market, but that will only provide so much competition.
If it supports DDR5 at all, then it should be at most a firmware update away from supporting 48GB dual-rank DIMMs. There are very few consumer motherboards that only have two DDR5 slots; almost all have the four slots necessary to accept 192GB. If you are under the impression that there's a widespread limitation on consumer hardware support for these modules, it may simply be due to the fact that 48GB modules did not exist yet when DDR5 first entered the consumer market, and such modules did not start getting mentioned on spec sheets until after they existed.
You don't want to use more than two slots because you only have two memory channels. The overclocking potential of DDR5 is extremely high when you only run two DIMMs. All the way up to 8000. Meanwhile if you go for populating all four slots, you are limited significantly below 5000. Almost a 50% performance drop if you are willing to overclock your RAM.
If you want to run something that doesn't fit in 96GB of RAM, you'll get better performance from having enough RAM. Yes, having two dual-rank DIMMs per channel will force you to run at a slower speed, but it's still far faster than your SSD. The second slot per channel exists precisely because many people really do want to use it.
In the specs yeap, in practice hardly anyone got it working. As far as I saw in reddit, it requires customizing timings to make 4 slots work over 6000 Mhz at the same time.