I use Ubuntu touch as a personal device, which has zero support for banking apps, meaning I have to have a backup Android device. My work phone is a pixel 6 running graphene OS, which manages to run all of my banking apps just fine. (Though admittedly I ‘got lucky’ in the sense that my banks are supported by graphene OS)
Graphene, or any other alternative to the big 2, aren’t perfect and don’t cover all banks, but graphene is by far the frontrunner for a viable alternative. If you haven’t toyed around with it and get the opportunity, id definitely recommend it.
I really hope we do see further Linux phone development, but without buy-in from the banks themselves, they will not be supported for the same reason Graphene isn’t. The only difference is Graphene allows sandboxing play integrity to navigate the “Google has to say it’s okay” nonsense. It’s a rock and a hard place problem; the banks won’t support without mass adoption, and mass adoption won’t happen due to lack of banking support.
I think sailfish OS has a similar integrity sandboxing concept, though I haven’t tried that personally, so can’t comment on how well it works.
Sure, variations of it will probably be. In the same way a fork of mastodon is used for Trumps truth social platform, despite it being a predominantly left application.
The key thing you’re not considering about open source is the lack of central governance. Ubuntu can decide to impose age checks, arch could decide it requires TPM setup, and fedora could choose to move to a licensing fee model. All would be independent decisions however, and only affect the respective distro and any built from it, yet they’re all called Linux.
Besides, with all open source applications, anything implemented can be reverted by someone else. The code is licensed publicly for this exact reason.