In narcolepsy type 1 (NT1), patients have severely diminished orexin levels. This appears to cause them to inappropriately enter REM sleep.
OP notes that the mutation lowering the sleep requirement causes an increase in orexin. I wonder whether the increased orexin could be inhibiting REM and perhaps facilitating a more restful architecture of sleep. Alternatively, perhaps elevated orexin levels during the day cause wakefulness such that you just don't need as much sleep, regardless of how efficient the sleep is.
It would be interesting to compare sleep tracking data of people with and without this mutation to see if there are significant differences in time spent in different sleep stages.
As noted elsewhere ITT, there is a strong biological need for sleep, and its main role is very likely to reduce reactive oxygen species (though the amount needed vary by genetics) Orexin levels increase the noradrenaline ones, which is one of the few antioxidants able to reach neurons (along with melatonin) and by this way also increase slow wave sleep, making it more efficient. So yes, this could be a way they would need less sleep.
This stuff? Orexin receptor antagonists? They work. Holy crap, do they ever work. Sleep quality better than the Z-drugs, great tolerability, no massive disruption going off them... when these things go off-patent they're going to be massive. Sleep quality was not perfect (maybe 80% of "normal"? I don't know) but that is absolutely minor compared to the alternative.
(And for the record, I'm off them now due to other stuff clearing up such that I don't need this level of sleep assistance anymore. Not because I can't afford them.)
I guess that's a long-winded way to say that if you're going to do questionably-advised sleep biohacking, orexin receptors are probably the place to start.