There are always rumours about a P?. If the latest is the P4, then a P5 is rumoured. DJI will eventually leak a preview of it to someone, but really? listening to rumours on Facebook......
The demise of the P3 has little to do with whether a new model is coming, DJI are simply using up parts until they can't make any more P3s.
Very curious; from the DJI / Consumer / tab under Phantom Series you see "Phantom 4", "Phantom 4 Advanced" and "Phantom 3 SE". When you select the Phantom 3 SE you land at that page and it seems that you have found all the Phantom 3 quad-copters that they have available. But, look critically at the left and right edge of the screen (where many photo viewers have the "next" and "previous" buttons. Grayed out are the navigation buttons that will take you to the other Phantom 3 aircraft...