Hm, as a starting point, maybe we should investigate the relation between hours of sleep/day and Alzheimer's. This may or may not provide additional insight. Certainly there are people who seem to need less sleep than others - they may have higher (and longer) levels of orexin.
Another topic: the relation between modafinil and orexin. Right now, the relation is unclear. Modafinil seems to activate orexin receptors, but it also seems to act independently of the orexin system. It might be possible to coadminister an orexin antagonist AND modafinil, to maintain wakefulness while reducing orexin levels. Of course, we still know little about modafinil's long term effects.