What fills the void now is what has filled the void for years. The plethora of Endgame content available in FFXI. Dynamis, Limbus, Nyzul Isle, Assaults, Salvage, Sea, Sky, Einherjar, Dreamlands, ZNMs, VNMs, Abyssea, Voidwatch, and Ultimate (Relic/Mythic/Empyrean) weapons.

For a new player who hasn't had the opportunity to do all of the content I listed above, you would be doing yourself a grave disservice if you were to ignore previous endgame in favor of just spamming Abyssea. Old gear is still relevant in many cases, there is a mountain of game lore for you to cover, and frankly the old stuff is still fun while being "easy" enough now that smaller, newer groups are able to complete them despite their previous "Endgame" status.

Leveling has been a means to an end in FFXI for a very long time. I think you will be pleasantly surprised with the kind of things you can do after reaching the level cap. Make a couple adventurous friends who like to explore the game and have at it.