[Question/Feature] Is IgnorePkg a viable workaround for safe overlay upgrades?

As per the wiki, pacman.conf has IgnorePkg to prevent upgrading certain packages. If one were to add all the Steam OS default installed packages to this list, would it be safe to run pacman -Su on the overlay, or is there some other issue that I'm not aware of? Obviously, I'm hesitant to simply fuck around and find out.