It would be great to see some more cross over events for previous FF’s, like the FFXIII event from a while back. Where you could do a series of quests to unlock equipment/hairstyles based on the characters from that FF. They could even add Egi glamours where you could make the Egi look like it’s counterpart from previous FF’s. Garuda could have Valefor from FFX as a glamour! That would be so cool!
The FFXI, FFXIII and DQX events were actually exceptions rather than the rule, as all three events had a deeper connection to FFXIV’s development than just fan service. They were event that actually all celebrated certain milestones in each respective title, and also had a deeper meta connection to the development team.
Specifically, the FFXIII event was actually a result of an in-joke between FFXIII’s producer Motomu Toriyama and Naoki Yoshida – where Toriyama included miqo’te racial gear and the level 50 GC GLA/PLD weapons as equipment for Lightning in Lightning Returns ~ FFXIII, Yoshi-P famously stated at E3 in 2013 that, paraphrased, he “would find some way to repay the compliment” by “finding a way to have Lightning appear in FFXIV ARR” – officially though it was billed as being cross marketing for Lightning Returns.
Similarly, the FFXI event was to celebrate FFXI’s eleventh anniversary of service (a similar FFXIV event involving spriggans was held in FFXI around the same time), as well as possibly being a fond tribute to Hiromichi Tanaka, FFXI’s original producer as well as being FFXIV’s original producer whom Yoshi-P replaced due to FFXIV version 1.0’s disastrous launch (which ARR was the reboot of). FFXIV was also meant to be symbolically FFXI’s spiritual successor.
And finally, the Dragon Quest event was to celebrate DQX’s first anniversary of service, a game that Yoshi-P was originally on the development team for (before he joined the FFXIV development team as producer and director).
Thus, because of this, I doubt very much you’ll see any other direct crossover events to any other FF game, (specifically, SE already stated ages ago that they ‘have no plans’ to do crossover events for FFVII or X – the HD re-release of the later has already long came and gone without any crossover event occurring so sadly that’s pretty much the proof right there.)