Horntail?

First 30 people to enter can horntail until next SC. (Solo only)

Could somebody give a few more details of how this works?
I thought you needed to set up an expedition, same as Zakum.
So is there no longer an expedition requirement, or do you really mean that 30 expeditions can sign up, but only the expedition leaders can go in to solo?
Or do 30 HT solists band together and sign up as a single expedition after server check, and any member of that expedition can solo later, as long as the expedition is preserved?