Low price isn't some magical requirement for an HTPC, people tend to spend more money on their home theater system than a desktop gaming computer. What people want in a HTPC setup is low noise, low temperature, and compatibility with all the other components. With the new cards coming in at such low (rumored) TDP, noise and temperature tend to follow behind, especially with the Titan cooler. Coupled with that low TDP comes performance, supposedly one of (if not the) best single-GPU cards out there. Lower power requirements means a fanless PSU is possible.
Sure, you could use a 295x2 for an HTPC. Why not? Might be a tight squeeze in an HTPC case, but doable. Fanless PSU is questionable. That extra power is converted into heat, remember, and heat is not HTPC friendly.
HDMI 2.0 is a great addition to these cards, but for HTPC the receiver also needs to be HDMI 2.0 compatible. These are pretty new, so unless the receiver is wired for sound only, it would be required for the HDMI 2.0 4K TVs.