Ending spoilers: Lestallum was the only place where life could survive during the the 10 years of darkness, and that was only because the meteor site could be used to generate enough power to keep powerful lights on all the time. Basically all life on Eos that wasn't there was screwed. Hence no more beasts or wildlife around, no more people at Galdin Quay or anywhere else, the Starscourge turned them all into daemons. The Astrals no longer need to interfere with man, they don't need to give them magic to fight or heal the Starscourge.

It's like the developers wanted to make sure no sequels could be made, so they killed off as much as they could and left as few loose ends as possible (barring the ones meant specifically for DLC) and nowhere meaningful to go with the story after the ending.

The closest thing we'd ever see to a direct sequel I think would be something like FFX's audio drama that can be heard on the FFX|X-2 remaster. Unless an alternate ending is added I don't think there's anywhere to really go.

Personally I think it's for the best. Tabata can focus on Type-Next, Nomura can focus on VII Remake and KHIII and hopefully someone like Ito will be handling XVI. Or they can make some of our dreams come true and do a massive AAA FFT remake or sequel (we can dream).