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.
At the moment, we don't know if the leaked HTC One X9 promo image seen below is showing the real device. Hopefully, we'll soon find out more about this, as well as about the One M10.
sources: @LlabTooFeR, @evleaks