Plus, ATMs (at least where I live) run on stone-old machine usually which you would expect Linux might even be easier to run on.

I can't think of anything in terms of reputation that might hinder this movement. What did you have in mind exactly?

The question is if anyone has gotten their hands on the few different ATM machines hardware-wise and wrote Linux drivers for them. Basically the market for these, magstripe and EVM cards is very much a Windows market => at least most of the US providers of services, backends, software etc for this all are almost entirely Windows based. And therefor the manufacturers, although it would be easy for them, have not much incentive to deliver proper drivers. I'm not saying it's a big problem per-se, but it might make people nervous anyway.

They also need to be complaint and that can take long on new software, so they would need to pull in a provider who already has the compliance in some related areas, probably Redhat has and then try to tape on the extra compliance needed for the new software, drivers and whole combination.

All in all, it's all very possible, but I think going public with all of this is unfortunately just a trick to get MS to play. I hope it's not as I have always wondered, as a software engineer who created banners, POS systems and information panels (I don't know the proper English jargon for these; I know the Dutch names, but like the panels you see at events, train stations, airports :) why they are not using Linux for everything anyway; everyone always cries about drivers but those have been a non-issue already 10 years ago. 'They are used to writing software on Windows' has also always been a none issue; these apps are complete, fullscreen apps which are the only thing running next to the kernel and a few drivers on these systems. They are almost always completely custom drawn and, like 2D games, that means the difference between Windows and Linux is not really there and hasn't been for many, many years now. You can run SDL straight on the framebuffer and make a tiny Linux distro with your software/drivers to run on it.

We sold Linux POS systems over 10 years ago; built on C & Tcl/TK they were faster, easier, cheaper, and nicer than the Windows versions at that time by a long shot. There is 0 reason why you wouldn't do this, but people are ignorant and unfortunately many of these people are coders; like people are stuck on Linux & Mac, a lot of people are stuck on Windows and lose sight of what is better for the customer (over 10 years ago that would have been stability and price; both much better under Linux) while peddling the 'everything is better under Windows'. I would not expect that from smart devs but he, here we go :)