Currently, the update process of NetBSD is rather tiring, though it could be made easy. freebsd-update(8) does the same for FreeBSD, but it requires a special structure on the server to run. Either porting freebsd-update, or writing our own update client is the goal of this task.
Though there is already sysupgrade by jmmv, it has some shortcomings you should overcome. The new tool should be easy to use, able to check if there are actually upgrades, and be implemented in daily(8).
This task is not only about writing code (which will actually be rather small), but about testing it, and researching what you have to take care of to make the upgrade run smooth.
You should also have a look at the live-upgrade project, which aims higher than this one, but is different: A system upgrade is actually about performing binary upgrades of the system, while a live upgrade should only perform the wrapping around making an upgrade directly bootable and saving the old system.