Popular X-Plane video content creator Thomas Rasmussen has published a trailer for the Flight Factor 757 Flat Panel Display System (FPDS), indicating that release of the upgraded avionic set is not far away.

Additionally, an image of the FPDS was posted two days ago, confirming that the private beta run was "coming to an end":

The FPDS avionics will be a paid upgrade for existing customers of the 757, and will later be integrated into the 767.

Additionally, Flight Factor published a set of images showing improvements to the exterior of the airliner, which will be free for existing owners. For more details, see the article below.

Flight Factor is also considering development of the Boeing 777X and/or the Boeing 787, as confirmed in this reply to a Tweet. Nothing concrete has emerged regarding development for either aircraft however.