[suyjuris]

Instant typesetting would be very welcome – I have often wished for exactly this. But I do not think that it is a technical problem. TeX is very fast, after all. (As you would expect with software that age.) Rather, people do complicated things and those become slow at some point. If you cannot do complicated things, the system will likely not be popular, and the popularity of LaTeX is its main appeal, I think. Everything is just a package away. Perhaps it is possible to aim at another point on the pareto frontier and have something fast with fewer features, similar to the relationship between C and C++. Anyway, I hope I am wrong and wish you the best of luck!