The largest barrier to good layout on the web is that you can't measure text. All you can do is measure a node that has a specific text, which takes a long time

The largest barrier to good layout on the web is that you can't measure text. All you can do is measure a node that has a specific text, which takes a long time and includes a reflow, which means either a) abysmal performance, or b) an entirely async layout algorithm, which would be much more complicated.