I'll start: Pokemon Black & White 3. We never found out if N and Hilda/Hilbert reunited again! It's currently Pokemon's greatest cliffhanger, and it doesn't require a contrived "save the world from evil team" plot to make a compelling, 30 hour story out of. Also, as a fantastic send off to Unova region. Cheren x Bianca could be canonized, Bianca takes over as the new Professor, Alder finds peace, the three dragons restored to their original form, reconstruction of the Unvoa region and final dismantlement of Team Plasma... there's so much material they could mine here.
Another one: Final Fantasy XII-2. Vaan, Penelo, Baltheir, Fran, and Montblanc embark on yet another adventure, and we get to see the aftermath of our actions in the first game. We could explore Rozzaria or the continents touched upon in FFTA and FFTA2. Ivalice is by far Final Fantasy's richest setting, and it's just a shame that there was only a single console game for it.