I'm already at my endgame. If you mean when do I want to reach the same endgame the rest of the playerbase is at, the answer is never. By the time I register my copy of Heavensward, you'll probably consider Stormblood to be obsolete and be a few patches of the way in to whatever the next expansion after that is.
There's still a ton of stuff to do in the game I'm already playing. Once I finish it all and need to look elsewhere to have content to do, then I'll register Heavensward, but before that, I'll have at a bare minimun:There might be a few other things. There's some notable achievements, for instance, like the ones that reward the Luminary tools for DoH/DoL, that I'd want to do. I can't think off hand what similarly notable achievements there are in other parts of the game, but there probably are some.
- All jobs/classes to 50. (So far, I've just got BRD, NIN, and all the DoH and DoL there.)
- Have run every dungeon, trial, and raid available at level 50. (Still a long way to go here. I've done several hard mode dungeons and trials as I get to them in the course of relic upgrades, but most others aren't even unlocked yet. Haven't even started on Coil.)
- Complete every sidestory and sidequest in ARR. (I've done most of Hildibrand, but only just started on Moogle Delivery quests.)
- Have at least the first stage of all 10 Relic weapons, with at least one of them (maybe more) advanced all the way to Zeta. (Currently on the animus books for both NIN and BRD.)
- Max reputation with all ARR beast tribes, and complete the allied beast tribe quests. (Ixal, Kobold, and Amalj'aa done. Working on Sahagin. Barely started on Sylph.)
- Have all master books and Lucis tools, all earned from items I've made/gathered myself. (Just gearing up for this. My earlier attempts to make HQ Vanya silk for my first master book, back before I had good level 50 gear, didn't go so well.)
I'm already a bit flooded by all this content that I've yet to complete. Piling even more on top of it with an expansion is just way too much until I clear out my current stuff.