It is also worth pointing out Joel says "don't rewrite" specifically in the context of a software company, where I strongly believe it is largely correct. In the context of a decades-old open source project the decision may be quite different for legitimate reasons.
I find it likely that you'd be better off performing an algorithm extraction and doing a true from-scratch rewrite than trying to incrementally translate TeX and LaTeX.
But I don't think Joel is against a slow, one line at a time, working on the old code base rewrite.
It is not clear what kind of re-write the OP is advocating. But I would be surprised if he is pro the start from scratch kind.
But it might be just my biased perception.