I'm not really that surprised about windows 10 only for PC. Support costs, the fact that it's increasingly difficult to get drivers for older windows when buying new hardware, API support, etc. It could be many things, or really all of them that could ultimately lead them to this decision. I'd rather them say Win10 only now and then expand it when the requirements are solidified than promise Win7 and then backpedal later. Although, I have my doubts they'll choose to support more than Win10. Don't get me wrong, not advocating Win10 here. Not a fan myself. In fact I really wish there was confirmation on a native Linux version. /shrug. It's likely to work with little or no tweaking under wine, dxvk, etc. So it's not the end of the world I suppose.

There's literally no information on anything.

Minimum system requirements:
System:
TBC

So just wait. For wine + dxvk. Even if it will be the worst case scenario we have a year. In a year things can change drastically. Like Wine will get DX12 support enough to run the game at full speed without bugs, either in main trunk or with some external libraries like dxvk.

Also despite all good things i won't pre-order anything because right now it's a total black box. What if not only my workstation class laptop won't be enough but what if 24Gb video card will be enough only for low settings.

Which is unlikely, most likely the game will have requirements slightly higher than Witcher 3 but that's about it. It will be much bigger though, like FFXV/Doom 2016 size.

...unless you have an AMD video card, they stopped supporting win8.1 awhile back. If games stop supporting win7 I would not expect the win7 Radeon drivers to be of much help for win8.1 users..

It kinda sucks that win8.1 boxes are effectively being forced into early retirement before the current gen consoles which I appear to be outperforming. E.g., win8.1, i7-4790 with 16G, an RX 470 with 8G (the only upgrade) and I'm easily playing a recent release like Metro Exodus at 1920x1080 on Ultra quality and getting somewhere between 30 and 60 fps.

Just read on the (rather serious) German c't (computer magazine) homepage (heise.de) that they published system requirements and it mentioned Windows 7 and fairly moderate HW.
No word about Linux yet, but at least W7 so W10 doesn't seem to be mandatory.