[daeken]

I'm not sure that's the best guess. While it would be the obvious choice, I don't think much could be said to be "earthshaking" there, and Knuth isn't one to throw out hyperboles. I think it will be something new, almost certainly in a different field, and it will involve looking at an unsolved problem in a way different than it's previously been approached from, much like TeX. I can't wait to see what he announces.

[fhars]

But then, it is not announced as an earthshaking announcement, but as an "earthshaking announcement." The quotes make it sufficiently vague that it could be anything from "there was a typo in a comment in the metafont source", to "Vol. 4 is off to the printer."

[michael_dorfman]

Vol 4 is off to the printer. He's already announced that the first 5 fascicles will be appearing in hardcover later this year.

[ErrantX]

I'm willing to bet that it is not. The words are in quote marks which suggests nothing majority earth shattering (on the wider stage).

Probably a big TeX thing, given the context.

[studer]

It's titled "A Special Announcement!" in the TUG conference proceeding. I'd say the odds are pretty good that it's TeX-related.