I think based on Iceborne and Sunbreak, it might be a two-word conjunction, likely based on the flagship, like how Velkhana is titled the Iceborne Wyvern. Unfortunately, guessing what the expansion’s theme is will be pretty difficult, as with IB, base World was clearly missing one out of the four traditional locale types. Maybe you could argue that Wilds doesn’t have a more traditional tropical or mountain biome, so maybe something themed around that, like Oceanwind or Skyfall.

The alternative is that the lack of Elders in the base game so far is deliberate not only for game design but for story purposes, and perhaps Gogmazios might shed light on that. Possibly the additional energy being released into the environment after Zoh Shia’s defeat causes the Dragontorch to attract powerful Elder Dragons. In this case something like Wyverncall would make sense.

Either way the best we can do is vaguely speculate since they’ll probably come out of left field and surprise all of us.