I feel like it's fair to say that you have not "fixed the issues with browser layout" if you lose accessibility and input. System fonts I can live without, we can push our own, but those two things are a big deal.

Even input you might be able to hack around but accessibility is a big deal and the "hack" at that point is nearly to both lay it out in the browser and the supposed "fixed" layout system, and while that may work in some sense I again have lots of questions about whether that is really "fixed".

pretty sure I remember reading about this with excitement and wonder ...

That's part of the reason I'd find it so funny, yes.

The reason why I consider it a possibility is that LaTeX has two things out of the gate: The technical capability, and a small but arguably rabid user base. It's the sort of thing that can take an early lead but is quite unlikely to sustain it.

But you can't deny that LaTeX has had incredible staying power, despite the list of issues that everyone who uses it has with it.