How does it all work? Who gets the processing fees from the merchants running the Point of Sale?
The Bitcoin debit cards I've used exchange the Bitcoin at top up into fiat currency.
The cards are, internally, VISA/Mastercard pre-paid cards. You pay fiat money to the merchants, like on any VISA/Mastercard.
Who get the PoS fees? VISA/Mastercard/banks, as usual, I guess.
Does this help scalability? Nope. It's just a facile way to spend Bitcoin in a fiat governed world.