They're already doing it. See custom ROMs and Google Wallet. A lot of banking apps refuse to work. Then there's random apps like McDonald's that refuse to work on custom ROMs or if the device is rooted.
Banking apps I kinda get even though I think it's ass, but McD's??
The comedy is that my banking app refuses to use biometrics (after update), because it says I have ""not original"" ROM, which is false. If this goes further I will flash firmware just for that app to think I have original ROM.
I'm in a weird position where my Google Wallet refused to work with my original ROM (MIUI) since I had unlocked bootloader, but my banking app worked. It used to be that both worked with my custom ROM, but now Wallet doesn't work. I fixed that with Magisk + Zygisk + Play Integrity Fixer but then my banking app stopped working.
I mean't getting executed. Although I see your point. Either way I don't plan on going back to stock. Los grew on me. Sucks but you could get them working with a sandbox. I used Gbox for a while but decided to stop for privacy reasons.
Try Gbox or Google Space. Didn't try banking apps but stopped receiving custom ROM on WhatsApp Signal and some other apps. Highly recommend using shelter from f-droid
I wouldn't feel comfortable using Gbox or Gspace for banking, considering they don't seem to be open source apps. Then again, searching online, a lot of people seem to be saying Wallet and banking apps don't work with those solutions.
I'll probably have to settle with my banking app not working and paying with card.