Of course it could. But then, why would anyone do that? You can't compete with TeX on price, on correctness and quite probably not on quality of output. You're

Of course it could. But then, why would anyone do that? You can't compete with TeX on price, on correctness and quite probably not on quality of output. You're left with ease of use and performance. Not sure either it actually warrants such a huge undertaking as recreating TeX. This leaves open source typesetting a hostage of its own success.