> But, if folks tried more extension and less porting to a new language, I'd wager they could get far. This is what happens - pdfTex, Xetex, Luatex: these ar

> But, if folks tried more extension and less porting to a new language, I'd wager they could get far. This is what happens - pdfTex, Xetex, Luatex: these are all extensions of the core Tex implementation. The problem is that making these extensions is extraordinarily difficult given the software architecture of Tex. And, notoriously, sharing improvements between extensions is also very very difficult. The end result is that we have compatibility few improvements and complete stagnation is some aspects in the typesetting space (for example, no alternative/improvement to Tex's pagination algorithm). The problem is that Tex is architected as a monolithic application which you can't easily plug extra stuff into. All of the extensions to Tex have worked by forking the source code entirely, which I think is not a great model.