With the years a "Low requeriment games" means 8 GB of RAM and a i7 CPU, and in the future it will mean even more. But, I think it would be a basic solution to categorize the games with the three labels (low, medium, high). Just thinking if requesting all the devs to put the requirements is more complicated.
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I'd put it far lower than that. I had somebody messaging me a while ago on a some kind of celeron under 1.5ghz with 64mb graphics maybe 1 gig of ram. Pretty sure it was windows 10.
The bottom end would have to be Pentium 3 or 4 surely or an early 32bit core duo. There are also still PowerPC machine running modern versions of Linux. Single cores under 1.5ghz. Be rare to encounter but still out there being used.