A crossover between Final Fantasy XIV and Final Fantasy XVIs was finally revealed during the FFXIV London Fan Fest, and fans are already squealing over what was shown. For the quest introduced sometime in 6.5x, Clive is coming to Eorzea, and he's bringing some goodies with him.
Called 'The Path Infernal', the FFXIV and FFXVI crossover questline is coming in one of the next updates before Dawntrail is released. Square Enix hasn't announced exactly which one yet, just that it will come before Dawntrail. Based on what London Fan Fest showed about the event, the Warrior of Light will fight Eikons alongside Clive, the protagonist of the newest entry in the Final Fantasy series.

In the trailer, players saw a fight against the FFXVI's version of Ifrit in an area reminiscent of FFXVI. It's indicated by the trailer that acquiring Clive's glamour as well as a Torgal mount and minion will be possible during the event. Other collabs like this have already happened with FFXV and FFXIII.
This collaboration has been highly anticipated by fans of both games, and have been chuckling every time producer Naoki "Yoshi-P" Yoshida makes a joke about the director of FFXIV asking the director of FFXVI about the event. Now, players have an idea of what they'll be getting when the quest goes live, and many are excited to see how Clive takes to the many Aether crystals in Eorzea.
Players are also incredibly excited about the Torgal mount and minion that was shown in the video. Torgal is one of the staple characters in FFXVI, and fans were hoping that it would be an earnable mount sometime in the future. With the upcoming side-quest, their dreams of having Torgal as a companion in FFXIV have been made a reality.