This is just building a browser engine inside a browser engine, can’t see it happen.

Also unless it has the same feature as the level of accessibility it has no it would be a step back.

It would be a gargantuan job.

It's not a browser engine in a browser engine, just making the already existing browser engine available in another context. I bet that at least 90% of the dom implementation code will be shared (since internally the dom is almost certainly rendered through the same renderer process that also runs webgl and webgpu.