A new post on reddit has indicated that Rivals of Aether will be coming to the Xbox One "soon". Although, no indication of an official release date has been given, the game hit Early Access back in September, and was set to have a timetable of roughly six months before release. That would put the game's release sometime within the next month, if everything is still on schedule.
The developers also announced recently on their blog, that they will be hosting a Rivals of Aether tournament at GDC 2016 on March 16, 2016. The event is being presented in partnership with ShowDown, the Humble Bundle, and none other than ID@Xbox, so it's very possible that they could use the event to announce the release date.
Reddit users are already speculating that Xbox could promote Rivals of Aether in a similar fashion to how Sony did with Rocket League by having the game as one of the Games with Gold. Unfortunately, Rocket League's release date coincided with Sony's release of their free PS Plus games, and seeing as how Xbox Spain has already confirmed the Games with Gold lineup for March 2016, that is unlikely to happen.
Source: [reddit]