That's a great question. Right now the plan is to not remove old HoT gear from the store when the level cap is raised, so you'll still be able to buy the level 30 stuff. As for Brotherhood, we are planning to remove the level 30 gear from the store and replace it with new max level gear, so we're not 100% sure what we'll be doing with that trinket. We'll try to let you know with enough warning such that if it's going to be something you could miss out on, that you'll have time to save up and buy it.

We haven't fully fleshed out what a level-cap increase will entail at this point, but an upgrade system is one possibility. We do want to make sure that players can't immediately just have the best new gear upon reaching max level, so some amount of grinding or dungeon crawling or other work will be required to max out your gear again.