rewrite tex.web in C++?

Check Taco's CXTeX; "A hand-converted C version of TeX". I think one can throw some C++ syntactic sugar on top of it, but IMO that is as far as you can go without rethinking the whole TeX structure.

Have a look at the source code for LuaTeX: It contains no Pascal code anymore. All of it has been converted by hand to C.