Yeah I know Apple has their own WkWebview (maybe they were even the first? not sure). But as you pointed out, it requires devs to look out for any edge cases / missing features it has in comparison to Chromium's Webview.

The nice thing about a universal Webview is that devs no longer have to spend time testing across web engines. All they would have to do is test against a few generations of Chromium.

I know that's not a thing free software stans like to think about or hear because its already been happening in slow-motion, with less and less devs testing against anything but Chromium, but I feel there are strong benefits to it.

In a way its the SystemD debacle all over again. Centralization like that feels spooky and very un-unixy, but it brings such an enormous host of benefits.