

What a weird take. Alpha channels are used all the time. A lot of tools use WebP for them, though. Things like stickers and emoji in chat apps often recode into WebP or force you to figure out how to make a WebP with a certain configuration to accept your pack, but from there on out they rely on alpha channels.
MacOS app icons are a collection of layers with alpha channels embedded into them, stacked on top of each other, or themed individually. Unless you’re blind, any iOS or macOS user encounters alpha channels every time they turn on their screen. On Android, those files are even actual PNGs. On Windows, those are .ico resources, and everything larger than 64x64 is guaranteed to be a PNG embedded inside of an .ico (possibly embedded inside of a .exe/.dll/etc.
WebP has replaced jpeg for most web content already when it comes to compression. This just solves things like “how do I save my HDR images without degrading them every time I hit save”.
PNGv4/v5 may improve compression but it won’t be backwards compatible. It’ll get stuck in the same kind of limbo JPEG-XL is. Until that gets resolved, we’ll have to stick with AVIF/HEIFF/WebP.
I don’t really see the need for advanced compression in lossless files. You generally don’t download those in bulk without looking at lower quality previews anyway. Would be nice if the real file supports the same colour space the preview file does anyway. I’ll appreciate it when it lands, but I don’t think I’ll spend the hours converting my photo library to save maybe half a gigabyte of space.