I'd recommend all end-users jump to 5.5.1, there's literally no reason to stay on older fws any more. NUS-based offline updates are possible but probably won't be prepared for the initial launch. If N ships an update in the meantime, you'd be waiting unless you own a disk with the right update.
You can probably explain your way out of updating until the end of time but like... there's really nothing to lose by updating. Pinky swear.
Technical explanation: the main change in 5.5 IOSU (in hax terms) is that they verify SP is within the thread's specified stack addrs. If your SP is way out of range and you try to do syscalls, you'll panic. This is really trivially worked around in ROP, so it doesn't matter much. If you're (very specifically) a user trying to make exploits from public vulns who is also really bad at ROP for some reason, I wouldn't recommend you update. Literally everyone else should.