TeX and LaTeX set the bar high; it's hard to imagine something entirely new coming along and replacing them.
I've got a copy of Knuth's Computer Modern Typefaces (Book E in the Computers And Typesetting series, which I think is completed unlike TAOCP). I don't think many people get to see this book, and - indulge me - it really is worth looking at. You can see where some of Kunth's time went. Here's a quote from the preface:
Another piece of luck came my way in
1984, when I learned that the original
bronze patterns used to make the molds
of Monotype 8A were in San Francisco.
For years I had been working with
indirect and imprecise information
about the fonts that had stimulated
this work. First I had worked from
photographic blowups of letterpress
original pages from The Art of
Computer Programming; then Richard
Southall had prepared enlargements
from original proofs he had located in
England. At last I found the actual
80-year-old patterns that had
generated the metal type. The present
owner of these patters, Mr. Othmar
Peters, kindly consented to let me
borrow them while I was preparing the
final draft of Computer Modern, and I
learned much by measuring them with
calipers.
You just don't get that kind of attention to detail in many places, and that's why TeX endures.
