Most pistols models I can think of will be the same size between 9/40. So holster availability shouldn’t be an issue. Sure .40 is a bit more expensive than 9mm, but it’s far from cost prohibitive. For every person that’s “dumped” their .40 there’s been another guy to pick them up, so I wouldn’t be worried about being able to find ammo for the foreseeable future either. Well no more than any other caliber at the moment. I’m not trying to sway you either way, 9,.40,.45 all work just fine!
I'm in this camp here.
I'll add this.... most .40 platforms are more versatile than 9mm ones. They are a barrel swap away from 9mm or .357sig. It's not going away. I remember boys talking about 10mm being dead, only to watch it become popular again. All that being said, IMO, most of the best carry platforms that are compact, are in 9mm.