In fact, TT Games' latest job listing suggests that the developer's next major project is already planned out, even though nothing's been officially announced at this time. According to the listing, TT Games is looking for an experienced Senior Combat Designer, and there's a variety of information available that may prove valuable in figuring out what it is.
According to the job listing in question, TT Games is looking for a Senior Combat Designer to work on a new LEGO game that's going to be based on an established IP. Since The Skywalker Saga has already gone gold and will be coming out on April 5, TT Games has no need for new senior staff to work on that particular project. This alone makes it obvious that the listing has got to be referencing a major future release, rather than for something already announced and set to launch on such short notice.
TT Games' new Senior Combat Designer will work on designing and implementing the unannounced LEGO game's melee and ranged combat systems, as well as AI behavior. While LEGO Star Wars: The Skywalker Saga previews point out that the game is a true modern release, with few of its predecessors' gameplay caveats, TT Games might be looking at ways to improve the new gameplay systems even further in the future, especially if the unannounced game is a new DC or Marvel super hero title.
The fact that the listing goes out of its way to mention a "major IP" suggests that TT Games has got big plans for the future, no matter the franchise in question. While the studio has already worked on a variety of major IPs, such as Jurassic Park, Lord of the Rings, and, indeed, Star Wars, it's a simple truth that The Skywalker Saga could lead to unexpected collaborations in the future, as the game looks way more elaborate and promising than almost anything else that TT Games had previously worked on.
Since TT Games had previously collaborated with a wide variety of intellectual properties, guessing which comes next would be a pretty big bet at this time, especially as it would take at least a few more years for the project to come to its fruition. Hideo Kojima recently praised LEGO Batman games, and the new tech used for The Skywalker Saga could be leveraged nicely for an advanced LEGO Batman title. Time will tell, however.