There is no doubt that the original Pascal/WEB implementation of TeX is a masterpiece and I have learnt a lot reading through the source code (both weaved and tangled) but it definitely shows its age. Most of the code deals with things like lower-level datastructures and memory management that would be vastly simpler or unnecessary in a more modern language with good libraries.
Have there been efforts to reimplement TeX in a modern language such as Python while keeping full backwards compatibility?
At various times I've endeavoured this myself and have made some progress but I'm interested if other work exists.