I think Ladybird has already surpassed that mark. Maybe not in 100% of attributes, technically modern Chrome/Firefox don't even meet that mark, but it's also already gone well beyond in most of them. This including that they are doing everything in house from the image decoding to the font rendering (well, on Serenity - for other platforms like Linux/macOS they have QT bridge their implementation to existing stacks).

Still a long ways to go to be a Chrome/Firefox for sure but that it's already beyond what you suppose might be possible is just the point of why it's its own kind of excitement.

That might be true, but if that's where we've found ourselves it seems like the best course of action is to start over with a fresh web spec focused on staying as simple as possible.

Browsers have never had a sustainable revenue model. If we're at a point where building one is so complex that it requires a massive resource investment we're setup to eventually be left with only one or two highly centralized and controlled browsers. That defeats the whole purpose of the web.