We don't know much about the next Mass Effect, but one of the facts BioWare has confirmed is that players will not be saving the galaxy once more as the first human spectre, Commander Shepard.
Even so, the developer has stated that some of Shepard's companions may appear in the game, which begs the question, what of Shepard him/herself?
It wouldn't be the first time this has happened in a BioWare game, as Dragon Age Inquisition players meet the protagonist of Dragon Age 2, Hawke. It's no secret that many fans were disappointed with the ending of Mass Effect 3 and despite the Extended Cut and Citadel DLCs, BioWare could give a Shepard a small role in the next game as a way for players to say goodbye once more.
Of course, this is pure speculation and while Shepard may not be back in person, it seems highly unlikely the Normandy's captain will go unmentioned at some point in the game. Only one ending of Mass Effect 3 saw Shepard live so it's something BioWare would need to balance narratively.
Either way, you can watch a video discussing the liklihood of Shepard making an appearance in the video below from YouTube channel FazuGaming.