I think that not raising the level cap at some point will kill the purpose of the game. It will raise... the story has to continue, new primals have to appear... (more) epic battles have to come, and more skills have to become accessible (i still hope for some kind of skill tree.... unless what ppl claim it was present in many FF games... why not on this one?)

If they keep going with item levels as you said... well guess what? lower item levels will become useless even more that it would be with a level cap raise because at least, you would need the items to help you leveling your char. Those quests based on item levels... what would they bring to your char? new items? like.. you'll end up with a char full item 150... but being level 50? doesn't make sense.

As of new gears we could get... it would mean either gear higher level (i repeat imo it makes no sense)... or it could mean new gears with different stat allocation. I would LOVE the latest option.... It would show that finally SE team understood they have to bring more diversity into their game, and this game needs it a lot Clone Fantasy14 ;p
So yes in this respect they could keep adding new gear sets without raising the level cap or gear level, it would give the oportunity for everyone to customize their character as they wish, finally the game would become interesting with more pve builds and pvp would have a slight chance of becoming something. -> this is called horizontal progression. They should take exemple on GW2 best game out in the market when it comes to that (and they didn't need 2years to add content and diversity.)