I believe your concern, while valid, only affects systems which are currently adding records faster than 1 per nano-second on occasion.
Also while technically true - it could technically break monotonicity (records added in the same nanosecond could be out of order) they'll still be all "near the end of the file, likely in the same page" such that performance implications are negligible.
As a general rule I would avoid any program making any assumptions about a uuid. Programs should treat it as an opaque binary random value. Doing so avoids any future incompatibilities.
Also while technically true - it could technically break monotonicity (records added in the same nanosecond could be out of order) they'll still be all "near the end of the file, likely in the same page" such that performance implications are negligible.
As a general rule I would avoid any program making any assumptions about a uuid. Programs should treat it as an opaque binary random value. Doing so avoids any future incompatibilities.