I think there will be a 5D Mark IV, as the 5Ds and 5Ds R were specifically mentioned as not being successors to the 5D Mark III. And as far as I've contemplated, the only feature I'm fairly certain the 5D IV will contain is a Dual Pixel sensor, as the full-frame compatible EF 24-105 IS STM suggests that their will eventually be a full-frame camera (or cameras) with which to use it on.

Otherwise, I'd expect some sensor improvements, but those have typically been very small (incremental) rather than revolutionary over the past several years. I'd also expect a small gain in resolution, but I wouldn't necessarily expect a huge jump in FPS (though maybe a larger buffer capacity if a new type of memory card is implemented), not because it isn't possible but because Canon will want to segment their market based on the FPS feature.

I think the 5D IV will have more video-related upgrades as video was obviously not a priority in the high resolution 5Ds/5Ds R. An obvious addition would be 4K recording and maybe even focus peaking. Other than that, we might see built-in GPS, but I have my doubts as far as Wi-Fi goes (though it could happen).