Comment by svat

Knuth does not think TeX is feature-complete: he said “it is axiomatic that any complex system can be improved”; the current state is just where he decided to stop and make his “responsible exit” (his term from a recent talk!) after about a decade of working on TeX and METAFONT. See his 1990 article/letter The Future of TeX and METAFONT (https://www.tug.org/TUGboat/tb11-4/tb30knut.pdf) where he writes:

> My work on developing TeX, METAFONT, and Computer Modern has come to an end. I will make no further changes except to correct extremely serious bugs. […] I strongly believe that an unchanging system has great value, even though it is axiomatic that any complex system can be improved. Therefore I believe that it is unwise to make further "improvements" to the systems called TeX and METAFONT. Let us regard these systems as fixed points, which should give the same results 100 years from now that they produce today. […] anybody can make use of my programs in whatever way they wish, as long as they do not use the names […] In particular, any person or group who wants to produce a program superior to mine is free to do so. […] Of course I do not claim to have found the best solution to every problem. I simply claim that it is a great advantage to have a fixed point as a building block. […] I welcome continued research that will lead to alternative systems that can typeset documents better than TeX is able to do.