Well that is extremely disappointing.
Unfortunately not much has changed in our stance towards supporting Linux in the last few months and there is one main reason for that. Since our birth over 5 years ago we have always provided full customer support for all games we have released. That is not going to change. For every game we release we provide a money-back guarantee: if we can't get the game working on the customer's computer with the help of our support team, we return the money. The architecture of Linux with many common distros, each of them updating fairly often, makes it incredibly challenging for any digital distribution company to be able to properly test the game in question, and then provide support for the release--all of which our users are accustomed to.
This is why you do what pretty much everyone else has done and pick only one distro to support, or a limited set of distros - and of those, only officially support the Long Term Support releases if a 6-month update cycle is too much to handle. Each distro should be treated as a separate OS in its own right, just like different versions of Windows. Just pick a few mainstream distros to support officially and let the community handle support for the more exotic distros.
Regarding updates: I've actually been paying attention to these (I always set to notify about updates but not automatically install so I can see what gets updated and when). Mint at least does receive updates more frequently than Windows, but it's still only about once per week and the kind of updates are basically the same as you get under Windows - i.e. pretty much just bugfixes. I don't see why this should be considered an issue though as these kinds of updates can just as easily - and they sometimes do - break things on Windows as well. Also I'm yet to have any Mint updates break anything, or if they have then it's been fixed quickly enough that I never noticed.
Honestly, based on my experience since I started using Linux earlier this year I think the the concerns that GOG has about supporting Linux are overblown. I have a *lot* of Linux games on the Humble Store and I've had basically no problems with them so far, even the ones provided only as a simple .tar.gz archive. I attribute this to the fact that Mint is one of the more widely used distros & in particular because it's based on Ubuntu (which most developers seem to be using as their main target distro).
Sure, we could probably release a client and sell the games and let Linux users worry about the rest. We don't consider it, however, a viable option for the business model we have followed so far. Apparently our model has its drawbacks, as we cannot make everyone happy, but, as of now, we don't plan on introducing Linux support in the foreseeable future.
You could, and you absolutely should.
Start by providing basic Linux support as an opt-in only beta feature and just provide the native Linux versions of games that have them. Bring it out of beta only when you feel that you're ready to provide the same level of support as you do for Windows/MacOS.
This would be a win-win solution; we get the native Linux versions of games where available, you get extra sales and Linux experience (including feedback/assistance from the more experienced Linux users here) in preparation for providing full support for whatever distro(s) you choose, and nobody gets to feel ripped off because it would be made very clear via the opt-in that Linux support would be limited. You've already indicated previously that you are not opposed to providing betas/prototypes with limited support so your reluctance to do so with Linux support is baffling.
There is currently no distributor that I know of that both supports Linux and requires every game they sell to be DRM-free. Certainly none as big as GOG at least. This has led to the ridiculous situation where a game is available on GOG and Steam, but if you want the native Linux version then your only choice is to buy the DRM'ed Steam version. And this is happening increasingly often as more and more developers produce Linux versions of their games; even the bigger developers & publishers are taking notice of Linux and some are already promising Linux support. It is stupid that despite all this GOG still refuses to support Linux in even the slightest way.