When I first thought of PS3 getting motion controls back in early 2007 based on the success of the Wii I thought it was inevitable for all consoles to add more motion controls to their next systems. Today there are many reports of MS & Sony preparing improved motion controls to their next gen systems.
While the Six-axis hasn't provided me with any great uses on motion I'm a believer that they could further improve motion controls in some regards. Like on the Wii I did enjoy Wii sports, particularly Wii tennis when I first played it. Definitely a simple and easily accessible use of motion that even my grandmother could play. But I really hope in the next generation they will keep the option of having regular controls for more complicated games that motion could be too confusing, tiring or gimmicky. Waggle to me is an good example of a motion gimmick. Meanwhile swinging your arm pretending the controller is a tennis racket is a perfectly natural movement for playing the sport and an excellent use of motion controls.
However, personally I would still rather relax on a couch when playing videogames. To answer your question I would buy the PS4 as long as it still offered regular controls.
