The mobile processor has taken leaps and bounds. Apple's M1 is entirely ARM-based, yet is will destroy a 3rd gen Ryzen CPU. Intel's 12th gen CPUs are ARM/x86 hybrids (main cores are x86_64 and delegates work to ARM64 cores, thus keeping the platform and instruction set the usual x86_64). BTW, the M1's weakest chip is about 10% more powerful the intel's i9 9900 series on single-threaded, meaning it isn't just clustering, this power difference is significant.I doubt that desktop OSes will vanish. On desktop PCs and notebooks you have a big screen, big keyboard - all that is convenient and sometimes the only option when you need some kind of work done (even gaming). Mobile devices are good, but they are not so powerful and their screens are quite small. So, I accepted this and simply enjoy alternatives to Windows. The important fact is that only Linux is flexible: you can do (or get) almost everything you want it to be, that is why there are so many Linux-based distros. Of course, there are downsides of Linux world (I mean as a software), but that is great we already have alternatives. Thanks to people who spent their time of life to do and continue to do that great job.
Screen size and peripherals are irrelevant, coz as I've said in many threads, we are heading towards docking our mobiles, which will connect to a monitor and other peripherals. Connective technology already exists for this, the only hurdles would come from number of devices connected affecting and affected by performance (I think bus speeds on mobile boards will be one of the biggest challenges).
Battery life as the biggest constraint, but using power-saving technologies and with the increase of lithium-ion battery capacity, I think this will fix itself (especially as the last of the laptops with removeable batteries start shipping with built-it ones and we keep shrinking battery size).
The future may be one that we dislike, but it is inevitable. People want more and more integration. My phone's speaker is superior to my laptop's and every portable stereo I had as a kid. That's just in a couple of decades. And technological advancement speed continues to increase. Like it or not, the mobile phone is set to become the Swiss Army Knife of your lifestyle.