MST uses a terminals existing magstripe reader to receive wireless transmission of card data. It's like an 'air swipe' you could say.
This has been touted as a great tech for retailers who might not have updated hardware for the new chip cards.
Problems are: banks, independent card processing services, have been updating their customers hardware for months and months. The new hardware often has mag stripe reader, but the focus is on chip. The US is behind the rest of the modern world by still utilizing mag stripe tech. The new EMV system uses the chip, but signature required. In Europe the chip/pin method us used.
Anyway the mag stripe is on the way out. Samsung bought the MST tech as a bridge solution between stripe and newer tech (chip, NFC)
Disney needn't bother supporting every possible pmt system, least of all a bridge tech already superseded by the tech used by the vast majority of its guests.
The point of MST technology is that it is not hardware dependent. It is not something that Disney can turn on or off.
I have used Samsung Pay, and everywhere I can access the magnetic reader (ie I don't have to hand my phone to a cashier) It works. It works well.
The only way Disney can refuse Samsung Pay via MST is by Cast member enforcement. The cashiers must ask people to stop... assuming the customer swipes their own cards. Of course if the cashier swipes the card, then enforcement is simple.
Its funny how many people don't actually understand MST and Samsung Pay.
On another point.. mag stripes are not going anywhere. They are cheap, and gift cards will always have them. Expect to see them on credit card terminals for many, many years to come. In addition ATM/Debit cards are not part of the EMV chip conversions (unless you can use them as credit). Gas pumps, ATM machines and a few other places will be mag stripes for a very long time.