Pokemon Ultra Sun/Ultra Moon will be the last mainline Pokemon games on 3DS

The following comes from an IGN interview with Game Freak director Shigeru Ohmori..

''When we were making Pokemon X and Y, we really were trying to push the 3DS system to its absolute limits – which is what we thought we’d done. But when Sun and Moon came around, we completely redesigned the system, and actually ended up pushing the 3DS even further to what we thought was the most we could draw out of it.

With Ultra Sun and Ultra Moon, we’ve tried to eke that out more and really, really push the system to its absolute limits, and we’re now feeling that perhaps this is the maximum of what we can get out. So we’re really treating Ultra Sun and Ultra Moon as the culmination of our work with the 3DS system.''