This probably depends on what you define as "endgame."

I feel we can safely assume it won't require anything from the Coil of Bahamut or a completed zodiac weapon.

But if it makes you continue on with the "Seventh Astral Era" story quests, some of them do require an average item level higher than you would naturally obtain by the time you hit 50. Currently the last main story quest fight requires a minimum average item level of 90. Because of that, you would need to do some of either the six highest level dungeons, Syrcus Tower / the World of Darkness, or buy soldiery equipment to finish it.