Alternatively, if there's serious demand for it I'm sure the market will come up with a solution. Motherboards with BGA-compatible sockets, perhaps. Or PGA sockets designed to accept adapters you can solder a BGA CPU into.
MB choice today seems to be rather simple for me: What _socket_ do I care for, plus what kind of slots and ports do I need (memory, pci-e, random ideas about the minimum required numbers of USB ports, whatever).
But for me the socket came always first. I upgraded my CPU quite often and would like to keep that option in the future. In the past there was no need to throw away your board for a faster (clock speed) CPU and it made sense to me that way.
Not really. You can use it to throw out motherboards that aren't compatible with the category to which your processor belongs. Which is probably a very loose category - "Motherboards which support socket AM3 CPUs", for example. That's just not a very fine filter - probably only vaguely more specific than "Motherboards which were released in the past 48 months."
In the cheap processor is married to the low-end motherboard and the expensive processor is married to the high end motherboard world you couldn't. To get the higher end features you would have to buy the expensive processor, even if you didn't need it.
I still have a few questions though. What will this mean for aftermarket heatsinks/coolers? I never run with the stock Intel/AMD heatsinks, will these coolers be permanently bolted on just like the processor?
And for motherboards featuring high-end processors, what will this mean for scenarios where the MB fails but the processor is still good. Will we just have to scrap the two altogether?
I think the issue here is that builders/gamers will be pushed into spending more. Right now you can get a < $100 ASRock board, pair it with a i5 3570K and a decent video card and you're off. Now you're more likely to have to grab a > $180 board if you want a top-end CPU.