>> we might have mainstream water-cooled desktops running at 5Ghz+ and more reasons for people to upgrade.

> Can you think of what those reasons might be?

Some applications that I would want that might need to wait for high-cpu (some high-memory and/or high-disk) to become more mainstream, since I want them all to run locally until FTTH reaches my part of the boonies:

A scanner I can literally wave a piece of paper at, have it process all of the ultra-high speed video frame grabs into a high-dpi scan, then reconstitute the scan into an appropriate LibreOffice document or PDF, with better OCR and better vectorization of raster pictures. Then I auto-file all my invoices, bills, statements, receipts, etc.

A personal digital assistant that transcribes, annotates, indexes and categorizes all of my conversations across all mediums (voice, text, chat, social, etc.). This doesn't need to be ML-fancy at first (except for the voice recognition piece), just lots of memory+cpu+disk to drive intensive, continuous indexing.

A millimeter-accurate 3D positioning system, using differential GPS off of a geodetic mark on my property, with relays of signals to indoors. This would drive my robotic chicken tractor, curb edger, and vacuum cleaner. I could keep a detailed inventory of household items with this, then query the house computer over a voice link the next time I forgot where I set down $thing (some RFID and 3D positioning integration needed here). Outside, it keeps track of exactly where various pipes, outlets, irrigation heads, etc. are located.

A software-defined radio that scans for chatter on interesting bands like police and fire, performs voice recognition on them, and pings me when it hears keywords about my neighborhood, street, nearby streets, or region when combined with other keywords (like "tornado").

A house computer that can tell whether or not I'm in the house or not, if I'm asleep, getting ready to sleep, or still undergoing my morning routine, at my computer, at my tablet, on my phone, etc. And do this for all occupants and visitors. Lots of visual recognition from lots of camera input. For myself, I want this information to drive what information is presented to me, when, and in what context. Bloomberg Radio after I've been up for 10 minutes, and after I've put on my headset, before my first call (incoming or outgoing).

A process that continuously combs through my Emacs Org agenda, and compares against my current "state". If I'm driving away from the house, and confirm a query from the computer that I'm going out to buy groceries and run errands for the day (the query is launched by continuously-computed probability cones narrowing possible agenda matches against my GPS position until a threshhold is met), and no one else is in the house, then automatically put the house HVAC system into energy-conserving mode.

A dumb robotic mechanics driven by updateable software in my desktop computer to fold my laundry, turn over my compost bed, rotate stop valves monthly/quarterly (otherwise they freeze in place, the primary challenge the automatic flood sensors face today), change HVAC filters, open and file incoming snail mail, etc.

Intensive AR to turn nearly all parts of my house into smart surfaces. "What's inside that drawer?" "What's behind that wall?" "What's inside that freezer?"

If we are talking only about pure desktop applications constrained to the physical desktop/laptop computer itself, then yes, you may have a point. However, when we include extending the reach of those systems to our environment, and there is an explosion of data to crunch, then today's typical consumer desktop computer (4-8 GB RAM, 2-3 GHz x86_64, 2-4 TB at the top end) doesn't have the capacity to manage all of those demands simultaneously.