> Even if you could get some traction, you're gonna have a bad time getting banks to support this OS

This already happened. Banks here in Brazil like to require an invasive piece of software (a browser "plugin", though it installs system services) to access their online banking websites. For a long time, this invasive software was Windows-only, so those of us using Linux had to either beg the banks to enable a flag to bypass that "security software" for our accounts, or do without online banking. The same for the government-developed tax software, which was initially DOS-only and then became Windows-only.

But nowadays, there is a Linux variant of that invasive banking "security" software, and that tax software became Java-only (with Windows, Linux, and MacOS installers, plus a generic archive for other operating systems). So things can change.