TeX is one of those bits of software that's so complex to replace, it'll take another few decades (and likely a few false starts) before we can get there.
The fundamentals of TeX's typesetting are amazing, but everything else is just bolted on. You'd probably want to rebuild it with its own, custom language, perhaps inspired more by modern XML/markdown rather than the old TeX language.
The biggest problem that we're going to have moving past TeX is that it's something of a standard for math representation in text. MathML never _really_ took off. Re-training millions of people skilled in typesetting math is going to be _tough_.
The fundamentals of TeX's typesetting are amazing, but everything else is just bolted on. You'd probably want to rebuild it with its own, custom language, perhaps inspired more by modern XML/markdown rather than the old TeX language.
The biggest problem that we're going to have moving past TeX is that it's something of a standard for math representation in text. MathML never _really_ took off. Re-training millions of people skilled in typesetting math is going to be _tough_.