A new typesetting system will be very hard to get people to adopt. There are a million packages and existing documents that would have to be ported over. At this point, compatibility with TeX is a critical feature, not just a nice-to-have.
New typesetting systems are a dime a dozen and none of them is getting anywhere. Also in almost all cases HTML/CSS is what you want to use anyway. TeX is pretty niche but it fills that niche perfectly. A 100% compatible LaTeX that plays nicely in today's infrastructure is all I want.
That would be a huge effort. Your time would be better spent designing and creating a new typesetting system.