Hypothetically, they could do it one of two ways:
1.) Have a piece of conceptual artwork, similar to the Osaka art, but instead of having a logo of USF or Islands, it's just the generic Universal Orlando Resort logo.
Or
2.) Announce the expansion plans with Super Nintendo World: Mushroom Kingdom, and say that more will be spoken at a later date with the piece of concept art.
There can be a third option however, if LC goes down by the beginning of 2019, they could perhaps go and announce Zelda and leave the Southern plans for a later time.