The irony isn't lost on me that in this article titled "Drop PNG and JPG for your online images: Use WebP" all but one image are in PNG format. Only the GIMP dialog box image is an actual WebP file.
And due to how the page is setup apparently, even that one WebP image Firefox (macOS) only shows in the web page but you cannot view if you right-click and select 'View Image' (as you can with PNGs and JPEGs), instead only offering to open another program or simply to download the file. (I say this as I have found other web pages with WebP images which let me do this just fine.)
Also, from what I recall, while the author talks about the % of compression vs. other formats, not mentioned is that animated WebP files, for example, require more processing power during playback compared to animated GIFs. So there's a tradeoff between download time vs. load time/CPU/power which impacts those on older/slower systems.
Mind you, I think the offering of this format is well intended. But the reality, beyond the quality of the image as mentioned, and as demonstrated here in this article online at opensource.com, is that it simply hasn't been adopted to near the level needed yet. One must eat their own dog food if they wish to make a proper case. But clearly doing so means reaching less folks. And so there we have the conundrum.
[To be clear, I'm not faulting WebP for this. It's a bit of chicken and egg. That is, it is in software akin to why in hardware we're all STILL stuck on QWERTY keyboards (for those of us in the U.S.), a keyboard layout/design intended to slow down typing in the days of typewriters with hammers. Though we've had decades to transition to more efficient Dvorak keyboards which would let us double our typing in most cases, we haven't. Changing your own keyboard is one thing, but when every laptop/etc. sold is still coming with a QWERTY, and you need to get work done and be able to move from computer to computer... Anyway, as WebP is more software, hopefully it won't take near as long. But even something like this takes time.]