I've been wondering how Mathematica Online would perform with either older computers or with some of the new tiny Arch.Linux computers. So, I took my kid's Samsung Chromebook and logged in. My experience was pretty good. Not as responsive as my i7 Mac, but acceptable. I also just logged in using an old Dell "Core Duo" laptop our IT department lugged out of storage. Once I realized that Online does not work well with Internet Explorer (3d graphics hang) and switched to Chrome, the experience was excellent. (3d graphics were a little sluggish, but not bad)
So, Online will basically create new opportunities for both older computers and for cheap little machines running Arch.Linux or regular machines running Linux. One won't need much internal storage because that's on the Cloud and one won't need much of a processor because most of the work will be done in the Cloud. I like that the cost of sophisticated computing will be reduced.
We could, by the way, have "reverse benchmarks," finding the worst-performing computer on which Online performs acceptably.