Is there an adjective meaning that an idea or object has longevity, or will still be relevant in the future?
(I believe I’ve heard such a word, but I can’t think of it at the moment.)
While this textbook is interesting, it does not seem particularly [?]; five years from now, it will be useless.
There are a number of possible synonyms:
eternal, lasting, permanent, enduring, abiding, immortal, everlasting,
ceaseless, immutable, indestructible, undying, ageless, imperishable,
The word required in your example, however, might be definitive, which carries the sense of being authoritative.