They used to say the same about games on 2D, time proved them wrong.
I've been around since the 70's and never have heard that being said about 2d games. Also, what we are talking about here is NOT the medium its the
tech the medium is played on. So making that comparison is apples to oranges. 2D games will never go away and any shred of common sense will tell anybody that. They are like simple low budget movies. With all the tech and big budget movies that exist, we still get simple low budget movies that with good writing, directing and acting can put many of those ridiculous high production movies to shame.
2D games are the same... a simple (or extravagant) well made, interesting, fun 2D game can still be successful and that will always be the case.
But many of the pieces of TECH that play 2D games like: snes, nes, genesis, all the Atari systems....etc etc those are long gone and the occasional "mini" release to cash in on nostalgia, doesn't count. That's what's being discussed here, not the medium.
The dedicated handheld console IS gone, It joins the VCR, the laser disc player, cassette players, 8-track players, the floppy disc drive ...and many more examples of a platform that a medium is played on that has fallen to progress. The video game and or style of video game... that medium itself is something different and it continues of course.