What linux or other system would you recommand?
To be honest Windows 7 is still perfectly viable.
The ONLY thing so far that I've found I can do with Windows 8 that is problematic (but not impossible) with Windows 7 is
the ability to mount .iso files and see into them. Unfortunately, this does not offset the many deletions of functionality one once had in Windows 7.
Given that, beyond the overt user manipulation Microsoft attempts, todays operating systems are more like the beta or even alpha releases of yesteryear, it might well be the right approach for you just to wave off Windows 8.1 for a while, start
thinking about Windows 8.0, and stay conservative by continuing to run (and order new systems with) Windows 7. Being completely frank, right now there are no real alternatives that would be anything less than incredibly painful
to switch an enterprise over to.
When does the advice to "run the old system and wait and see" turn to "OMG, we really really need something else"? Great question. We all have secret hopes that they'll get back on the straight and narrow and release an amazing
version 9, but the ship may just be too big to turn away from the icebergs. I think if we see something of Windows 9 and it seems worse than ever (or just no better than Windows 8) that's the time to seriously think about abandoning ship.
If keeping current is important to you, you could go with Windows 8 (.0). Windows 8 took until about mid summer 2013 to reach a level of maturity (e.g., by the heroic actions of 3rd party developers re-adding deprecated functionality)
that I wouldn't just throw it in the lake today if it came on a new computer system. So what's that, about a year after release before it's a viable candidate to be the basis for a serious computing environment?