So my unpopular opinion of the day: I really wish Game Freak would change up Pokemon's Hidden Abilities between generations more often.
Game Freak clearly are open to doing this when they judge a Pokemon's HA to be overpowered (Shadow Tag Chandelure, Lightningrod Zapdos, and all of the legendary beasts) or when it seems they realise they messed up by giving a Pokemon a HA it can't make very good use of (Quick Feet Scolipede). The most interesting case, though, is Gengar going from Levitate to Cursed Body. I don't remember anyone crying out for Gengar to lose Levitate at the time and Cursed Body, while a good ability, is overall a downgrade. But it seems like someone might have felt that Levitate was too good an ability for Gengar. That, or it may simply have been a purely flavour-based change since Gengar, uh... doesn't Levitate, and this made it ineligible for Sky Battles (but I doubt that it was purely done for flavour-based reasons, and Sky Battles don't show up after Gen VI anyway). I'd be interested to know if the reason for the change was ever addressed, if anyone knows.
But yeah, I'd be up for more tweaks such as this. For one thing, it keeps the game fresh. Much as certain moves or abilities sometimes get tweaked between gens, it shakes things up with each generation's competitive metagame and would give players more incentive to use older Pokemon. For another, it's a way to give older Pokemon access newer abilities without being needlessly complicated. Ability distribution needs a shakeup imo; Gen IV and V both shook up ability availability, but some Pokemon have had the same two or three abilities for multiple generations now. I'm not at all suggesting every Pokemon needs this: some (lots, really) are fine as they are, but some could use a freshening up.
Whether it has to be for Pokemon that desparately need them is not really the point - some Pokemon, like Delibird, could really benefit from a new HA, and others, like Salamence, wouldn't really be improved or nerfed either way. In the latter case, it's a strong Pokemon with two very good ability choices; it wouldn't be ruined by losing Moxie, and giving it a different ability would just give it a little extra versality. If anything, that'd be partially like giving it a new form. Not quite the same, but similar.*
*Actually, it's funny that I chose Salamence off the top of my head because it'd be a prime candidate to bring back Aerilate, since that ability is currently unused due to being exclusive to Megas.
So yeah. Game Freak have tweaked stats between gens, so why not abilities too?