What do you think the name of the next expac could be?

[Shurrikhan]

I imagine the localization will again be a single word, but ideally not a compound one this time, e.g.

Genesis
Terminus
Eclipse
Solstice
Arrival
Reckoning
Renewal
Etc.

It's worth noting that unless much has changed since the ARR interviews, the names of most settings, plot-lines, and job skills are actually made first in English and Japanese is one of the localizations thereafter. The expansion titles may well be an exception to this, making it very likely that the 'color' based theme will continue (Blue, Red, Black, ...[White?]), but different localizations can certainly give off very different ideas with their titles. Even on the Japanese version of the game, though, it's the English title in large font, with the Japanese tucked into the corner. Even if we know the Japanese will always two kanji (one of which is a color) + の + any number of katakana or kanji and the Chinese is always two characters (no color required; used only for Stormblood) + 之 + two characters, it doesn't actually give us clear clues for our own English title.

Heavensward --> Ishgarde of the (Blue) Heavens
Stormblood --> Liberators of the (Red) Lotus
Shadowbringers --> ...Villains in Jet Black... (I mean, really?)