"Applications should not access sysfs" doesn't mean there should be only one version of the intermediate library. There's already Systemd-Udev and Eudev versions, at least. For the case of Xorg, it just means sysfs access should not be hard-coded in the source of Xorg, but there should be some library in between, so that it is not necessary to recompile Xorg for every version of the kernel. So any replacement for the needed subset of libudev would do it.
Yes, but that's the whole point: the needed information is available as is in sysfs, and putting a library in-between is 100% bloat. It's just about testing something in the device path, and the device path is just that - a path in sysfs. The way libudev proceeds to get that information is entirely more complex than necessary - it even adds operations that can fail, such as memory allocation, when it is entirely useless here; but with the way the libudev architecture is designed, it is the only way, and there's no escaping the bloat, added SPOF, added failure points.
There is _no good way_ to implement the interesting parts of EvdevDeviceIsVirtual() without directly accessing sysfs. It's either sysfs, or libudev, or a libudev replacement that would, by design, necessarily be just as bad as libudev. -- Laurent
