I'm not sure if this would be possible or not, but perhaps adding a toggle for players to use their rested EXP bonus or not would be awesome. I'm leveling multiple classes simultaneously and only want to use rested bonus on a class I'm leveling with my friends in a static party, as we'd love to ding 50 on around the same mob. As it stands right now, if we're unable to get together, I'm unable to level anything else because I'd be losing rested bonus and would have to basically play catch-up, using leve allowances or FATEs.
This would be a fairly large QoL improvement for players looking to level multiple classes simultaneously and would allow them to utilize the Armoury system to a much greater extent, possibly increasing interest in the game and multi-classing.