gix12
But I must say as an app programming platform, flutter is brilliant. The ability to pass around statically typed classes representing everything from widget to text style to animation is so fast and logical, that it actually made me enjoy frontend programming. No need to mess around with html+js+css+some macro language to glue it together.
Did I mention i run the same flutter app on android, ios, web and linux box? I just wish they would use something like kotlin instead of dart, but still, it's well worth it.
But fair enough. In the wild you would have to use fallback pretty much always.
Still, webassembly-able gecko would be handy and would allow for experimenting with above mentioned streamlined 'web standard'. Web author could simply sign it's compliance to the 'standard' using meta tags, http headers or some other way.
Taking it further - the website author could possibly specify rendering engine it prefers to be rendered with(as specific version could simply be downloaded on demand from cdn, like common js/css libraries are). And pure webassembly apps (ie flutter) could skip the html/css/js bloat altogether.