It seems like there's a spectrum of outcomes here. As a user, I don't particularly care about system files, I care about the
state of the system. In fact, if all this does is protect system files, then a ransomware attack would just wipe out all my user files and revert the machine back to a fresh install-- an identical outcome to if I just reformatted the drive and reinstalled Windows. Not helpful!
Really, this scheme needs to include the entire contents of the drive-- "freezing" the restore points Windows makes automatically. Now the tradeoff is how often you annoy the user/how fresh the backups will be. Once a year is obviously too infrequent, once a second is too often. Once a week, or month. Maybe do it at the same time as Windows does a system update, as you suggest.
You don't need fancy hardware support for this, just a NAS backup box with a client that doesn't let you erase older snapshots.