Is it a fact that implementing fixed-width fonts actually requires a complete rewrite of all code and rethinking of the fundamental data structures? I think there's a pretty big gap between making a nontrivial change to an existing codebase and starting all over.
I certainly don't agree with Joel on everything, but I think he makes excellent points in the essay I linked above. I think every programmer maintaining a project hits a point where they want to rewrite everything. The code is full of hacks, the API is crufty, the requirements have evolved, etc. But that doesn't mean that such a rewrite is a good idea. And I bet we could all agree that a rewrite is not implicitly a good idea. All other things being equal old, tested code is better than new, untested code.
I don't disagree, but I can only assume Allan reached a point where maybe all the features/fixes to-be-implemented warranted a near-total rewrite as opposed to individually fixing or implementing them.
Plus, the CJK fixes in particular he's discussed literally now years ago were supposed to involve Core Text, which I believe was new to Leopard, which was then in turn a fairly new thing. Perhaps in addition to his shortsightedness/disinterest/whatever it may have been that he didn't consider that cjk would be an issue, new APIs and more made the idea of a rewrite more appealing.
I certainly don't agree with Joel on everything, but I think he makes excellent points in the essay I linked above. I think every programmer maintaining a project hits a point where they want to rewrite everything. The code is full of hacks, the API is crufty, the requirements have evolved, etc. But that doesn't mean that such a rewrite is a good idea. And I bet we could all agree that a rewrite is not implicitly a good idea. All other things being equal old, tested code is better than new, untested code.