Thinking back on my own childhood, which was filled with figures for near as long as I could remember... not many other kids played with or collected them past 1st or 2nd grade. I was born in '84. I remember wanting to play with figures with a neighbor in like 2nd grade, and he said something like "I don't know what to do with these" and we did something else.
I remember by 3rd grade a kid was being bullied for wearing Power Rangers paraphernalia because it was too kid-like. I remember being embarrassed that I still played with figures in the later half of elementary school when all my other friends had moved on a while back. I'd often hide them in my closet when a group of friends came over so they wouldn't laugh or think I was childish. It's possible I was friends with other kids who had figures but also felt the same social pressures to grow up and not be a kid.
By 4th-5th grade McFarlane had released his Spawn figures and they were kinda like a transitional line between kids toys and teenage culture. I knew one or two people that occasionally picked them up, but almost like desk art and not toys they'd pose around or play with. There was some respect on the idea of a "collector item." Sports were big, and kids were starting to get into music.
My micro-generation came in at the tail end of the Star Wars, MoTU, Thundercats, and we didn't really have those figures unless they came in through garage sales, older siblings, etc. But I remember Power of the Force figures, and the buzz with them were that they were collectors items (though I just wanted them as toys) and could be "worth something."
I grew up alongside the evolution of video games—Nintendos were ubiquitous and later the Sega Genesis, Super Nintendo, and so on. Those were popular, but my parents never allowed me to have a system. I didn't own a console until my 30's. I think even back then, gaming had by and large replaced the action figure. Maybe I kept playing with figures because I didn't have video games, just toys and comics. And the same thing could be said about comics, even back in the 90's most kids I knew didn't read them, let alone read them regularly. Or if they did, they didn't mention it.
That's all to say, I'm not really sure how younger generations will influence the adult collectors market. TBH I think it might be strong for some time ahead, but what IPs get figures may change. I think there are a lot of 20something collectors who are buying figures as adults that didn't collect or play with them much as a kid. Especially properties like Dragon Ball, but also Legends. Nerd culture is a lot more hip and permissible than it was during my young adulthood, and it's easy to find communities online. It's not unheard of for a guy in the office to have a Boba Fett helmet or a Mario action figure next to his computer. We're also in a unique era where we can easily stream media from different eras, meaning things may come in and out of vogue as generations rediscover dead IP and make them go viral.