Given the fact he's been given itty bitty buffs here and there I think they're planning on doing some tank nerfs at some point
They usually save pre-season for major changes and we're rolling up on it, tank junglers/tops have been meta for a while after Naut/Galio ate nerfs so they're probably going to do blanket nerfs to the class and it might indirectly bump Nautilus up in the tank class.
Personally tho if I wanted a buff in the short term, more shield value or lower cd on shield would be better. W has high damage over time as long as you still have the shield up, if it has less base than before but you can have more shields I think thats a fair way to keep in him the tank role.