2038: only 21 years away

Yes, it's been considered, and it's certainly one of the solutions that will be implemented in certain systems. But the Epoch start is part of many standards, so changing it involves an incompatible change, often creating multiple versions of the same standard that aren't distinguishable. It also means that the new systems can't handle data from the older systems; NFS3 should be able to handle the complete range of timestamps on files on the system, whether they be created today or extracted from an archive of Sixth Edition Unix.