I applaud you for attempting to spell
it out in so concrete terms. I think I understand
the argument, but
McDonald's then tries to buy supplies for 100 they got from B. There is no one who wants to accept their transactions as the economy is so small, there are no fries suppliers running nodes on network B. They are all still doing business on network A.
Is this a realistic assumption? wouldn't the fries suppliers have an
incentive to follow and open up an account on branch with McDonald's, so as
not to lose their large customer. And all the people with a liking
to hamburgers? Especially since they all - including McDonald's -
can still run wallets on the other forks.
I'm just not convinced that economic incentives are enough to
keep everyone on the same boat. To me they could under certain
circumstances encourage splitting. Please note that I don't think
this is a necessarily a bad thing at all.