1. Tetra Master
Triple Triad is fine and all but I'm sure there are people that enjoy Tetra Master too. Implementation is easy: Simply give all existing cards and future Triple Triad Cards Tetra Master stats as well (starting at the minimum), let them grow with use as they did in FF9, and let people play either Triple Triad or Tetra Master with the same deck rules we have for Triple Triad.
2. Replaying Solo Instances
This can be done like so: The Wandering Minstrel in Mor Dhona can help us recall our past battles in the MSQ (including expansions) so we can do them again as often as we want (no reward of course, just for fun). Likewise, each Guild Master can help us replay Class/Job Quest Solo Instances. For expansion Jobs this can be done by speaking with the major city's local representative (Gibrillont in The Forgotten Knight for DRK/AST/MCH and Kotokaze in the Shiokaze Hostelry).
3. Gaol Cell and Gaol Cell Door Furnishings
I mean really, isn't the concept of having a dungeon in your estate intriguing?
Bonus Request: Please give us a way to give all Jobs both BiS AND Glamourable gear! I cannot request this enough, even if every Job's gear has to be seperated like some of it already is, and both Lancer/Dragoon's and Rogue/Ninja's already are.