Multiple sources tell Autosport that both automakers are looking into being on the grid as early as the 2016/2017 season. Since the series already has its ten teams confirmed for the third season, Nissan and BMW would have to join an existing team for the time being, which is what Autosport's sources are saying is being discussed. Nissan refers to its consideration as a "fact-finding" mission.
BMW had said earlier that it wouldn't compete as long as mid-race car swaps were part of the practice. Formula E is looking to move toward a single car format as early as the 2018/2019 season, which could make BMW's direct involvement more palatable to the automaker. As for Nissan, it would have to garner approval from the Renault-Nissan Alliance to compete against its sister company in the same racing category.
Either way, it's unlikely that either manufacturer would be able to provide powertrain technology should they join teams for the upcoming season. Still, both Nissan and BMW have made strong commitments to consumer electric vehicles. To be directly involved in the competition would not only be a great way to showcase their prowess in the world of electric motoring, it could also help to bring more attention to Formula E.