The plug-in board for a mountable CPU would have to move that data as fast as the CPU. You are talking a FAST interface. An EXPENSIVE one. One that is FASTER that the FASTEST CPU since you'll be upgrading it.

As opposed to what? A full motherboard that was cheaper to make by far.

Intel will CRUSH the motherboard makers.

AMD is hanging on a thread.

The only reason Intel doesn't finish them off is that then they'd have to deal with anti-trust issues. Every time AMD comes out with a performance jump, intel giggles, and releases the next processor that they already had waiting. The days of the opteron kicking intel's ass are gone.

So what market place is next for them to eat? Every company that uses Intel CPUs can be replaced with intel motherboards, and intel gets all the profit. They will scramble, and attempt to compete using AMD chips, but the global package of a default motherboard with default graphics and default network connection from intel will satisfy 95%(+) of the market, and they will do it cheaper than selling it to a MB maker who then integrates their chosen chipset.

The few INDIVIDUALS who care (and they are VERY few) will not pony up for those swappable CPU boards. Those are HIGH end equipment. And those on the other side of the equation already are spending big bucks, no reason to make them cheaper until AMD comes up with something that competes, and even then it doesn't matter since the vast majority of big spenders will go for the known long living company, not the one that could disappear tomorrow if intel chooses it.

Follow the money, not the technology.

But the vast majority of current operational software is still wintel. It'll take more than a couple of years before ARM is running MS software in any usable fashion.
And every ARM advance that eats into the x86 market usually has a corresponding speed jump and power savings on the x86 side.

20 years ago everyone thought that mainframes would die due to price/performance, but very few people accounted for the incredible inertia of companies running software that would NOT be rewritten for anything else. MFs are still going strong. Old windows PCs have the same issue, running old software that runs businesses and no one want to pay to rewrite/move to anything else.

And even then, intel has rights to the arm and can kick them out at a high volume which means both cheap and high profit.

It might not make a difference when it actually does,but now, and for at least the next 3-10 years it does. Until then there will be the hard separation of the 2.

And intel will own it by virtue of producing 90+% of all x86 chips that make a serious profit. And then not allowing anyone else in the production chain to make any money. They can drop their prices and still make money while driving selected other companies under. All the wannabes nipping at their heels will have slow low priced chips that barely allow them to live, while intel owns the market and sets the rules.