A job description was posted on Gamasutra for a ‘Senior Level Designer’ and stated:

This obviously reaffirms what we knew already about ‘Titanfall 2’ but it also shows that Respawn is preparing to branch out into other video game genres.

There have been previous clues that can prove this is the case. In 2014, it was announced that the developer was splitting its resources into two groups, one of which was working on a non-Titanfall related project. As this IGN article states, it is possible that God of War 3 director Stig Asmussen is leading the project having joined Respawn in June 2014.

Regardless of who is leading the team, this secret game is unlikely to be released until 2017 maybe even 2018 but it is probable that more information will be released at upcoming conventions such as E3.

Respawn Entertainment are secretly developing a new 3rd person action adventure game - 74