Can see it being useful in spreading...well...Role actions about.

As a Tank, I'm thinking you may be able to have one 'set' that is primarily highly defensive, while the off-tank may take things that give a bit more punch or utility unless they know they will be needed for serious tanking.
It could be really interesting, or we may end up using the same things all the time. Saw the one that looked kind of like the current Ninja one that transfers aggro you generate - that would be an awesome one for an off tank at the beginning of a fight to help build the main tanks threat.

Either way, that people will be able to start as Marauder/Warrior, and get everything they need along the way, will be a huge step up from the current system where people have to level different things to continue on properly, particularly when folks are enjoying themselves then get forced back to level 1 to unlocked a job, possibly playing a class they have zero interest in ever using at all.

It does also mean that in the future we will have a baseline knowledge of utility that new Jobs will provide for definite, before they bring any Job based flavour to the festivities.