I mean, they seriously done many things in Windows 10 (and analogous servers) to improve security without too much breakage, like moving font processing from kernel-level to user-level (n.b. in the process, they have thrown Adobe code). Print spooler is tricky though: even if the official design of the API theoretically allows it to run user-level, ask users of HP products (including business ones) how many times their computer crash due to weirdness in HP drivers. (Why does the HP printing drivers run in kernel-level mode? I don't know!) I'm pretty sure that
nothing will happen when the spooler is moved to user-side processing, right? (In all seriousness, the drivers will break and probably crash the system. These products are officially out-of-support, so short of Microsoft paying HP to revamp the drivers nothing will happen.)
In all probability, probably even Microsoft is contemplating such move but breaking a lot of stuff is reputationally damaging to them, even if it's not really their fault in this case. Removing SafeROM is easier because it's just grumbling gamers who can probably patch up Windows 7, but imagine the support calls when the print spooler, a critical component, is moved. Even when a rational mind would put the blame on HP (et al., it's not just HP designing "weird" drivers), the problem will appear due to a Microsoft change and therefore Microsoft gets the blame.