He can't, but he can take notes from other video games in how they manage their endgame. A lot of MMOs and MMO-lites have an endgame treadmill that players can engage in, which is more or less just ilvl treadmills where it's a lot harder to grab your BiS.
The problem I see is that the game isn't really built for that. FF14 is a game that's designed in the opposite direction of pretty much every MMO. It's a very simple game where you go in, do the thing you want and unsub, and then resub once there's new content that you're interested in. It's basically the home for the burnt out MMO player, who's just tired of grinding and grinding.
A LOT of the content in the patches are released as if it's a single player game. It's very much so an "enjoy once or twice" and relies on the playerbase to build their own replayability around said content. Raids are only replayable because FFlogs is a thing and speedrunning and leaderboards is a big thing for people. Housing is only "replayable" because RP venues and social events are a thing, and imo there's nothing wrong with that.
Since they don't really want to alienate their core players (yes I know they already did with the job design, but bear with me) the only type of dev supported content that fits the game is content that infinitely scales, but doesn't give player power, PvE modifiers. An expanded Deep Dungeon system, and affixes that gets harder and harder that applies to both Dungeons and Raids (akin to the WoW M+ system) that has an in-game leaderboard, cosmetic rewards and/or titles, but no gear rewards.
PvP players already have a type of repeatable content with the old Feast and new PvP ranked. Crafters/Gatherers technically had this with the old Ishgard Restoration system (even if it is kinda mid, is gone now and doesn't really support Fisher). Social players can pretty much turn anything into something replayable with RP Events, Venues and even just plain hanging out in Limsa. PvE is really the only one area that's lacking, and that imo, is where the devs should focus on.
FF14 shouldn't turn into a gear treadmill type of game because it's simply not that kind of game.