Isn't the issue with Linux that there are so many different flavours and they can have major or subtle differences that could cause issues?
I've developed software for Linux before and what we did was choose specific common flavours of Linux to support, e.g. Fedora, Debian etc...
I see that there are a few posts that say if there is a Mac version then it's only a small step to Linux - but I do not think this is the case in reality or am I mistaken?
Not at all. Mac is relatively "easy" because it is a single, standard platform - you know everything about it. In Linux, there are more completely different distributions than political parties. And then, every box would be different from every other. The biggest problem are the display drivers - in Windows and Mac, you have the OEM-provider drivers, period, you know what you are working on. In Linux you will have people using the official OEM drivers, and people using the "alternative" reverse-engineered open-source drivers - these versions behave differently and the main difference is how they handle 3D acceleration. And guess what's primarily used for games?
I've been using Linux for some twenty years, but frankly, I would not think for a minute about using it for games.
ETA: and Linux display drivers all suck anyway, really.