Doubtful there's a script yet...seems to me they were still in the "brainstorm" process. I also wouldn't bet on the film being called The Muppets 2; that's just a placeholder name (they could have put "The Next Muppet Movie Which Doesn't Have a Name Yet" on the poster but it wouldn't have been as catchy). Once they know the plot/concept of the next film, the real title will follow.
If it makes everyone feel better, Great Muppet Caper was referred to as Muppet Movie II even after a script had been written, so again that was a placeholder name until a better one came about.
Even the last film had name changed until we found out that it would simply be called "The Muppets" relatively late in the game.
But it's cool to see teasers/promotion already as that just reinforces that the Full Plan is to get another movie made and they're not wasting time getting things going. That's always been the Muppets' biggest weakness since the late 90's: waiting too long to see how the last big project was received before planning what major project to follow up with afterward.