According to HTC ROM developer @LlabTooFeR (known for providing reliable information when it comes to HTC-related stuff), the One X9 will indeed be released next year, but it's going to be a device positioned below the One A9 - which is not exactly a high-end phone.
Reportedly, the One X9 - model number E56 - will be available sometime in the first quarter of 2016 (January - March). @LlabTooFeR has it that, 2 to 3 months after the One X9, HTC will launch a flagship successor to the One M9, which could be called One M10.
While there's no word on the features of the One M10, @LlabTooFeR says that most of the rumored specs of the X9 are wrong: there's no Quad HD screen, no Snapdragon 820 or MediaTek Helio X20 processor, no 4 GB of RAM, no 3500 mAh battery.
@evleaks seems to be confirming that the One X9 / E56 isn't a high-end smartphone, mentioning that its features should include a 5.5-inch display with 1080 x 1920 pixels, 2 GB of RAM, 16 GB of internal memory, 4 MP UltraPixel front-facing camera, 13 MP rear camera, and a 3000 mAh battery. There will be a MediaTek processor inside the X9, but it's not clear what model exactly.