It's not about the quantity, it's about the quality.
I doubt the majority of target 70D users need anything more than 18MP. In fact if 1DX owners are happy with 18MP then it clearly isn't just about resolution.
Given the poor showing this sensor gets from DxO (if that matters to you, not a jot to me) then the fact that the cameras built around it can still give very good results speaks volumes for the wonders worked by the digic processors.
A newly designed 18MP with digic 6 could be really something. Even the old 18Mp with digic 6 could be something.
I am struggling to think what features canon could add that would make the camera a must have. The last must haves for me were PAL video, manual video exposure, manual audio levels, wireless flash was great, and the flip out screen really handy for video.
The 70D will have to be really something to tempt me to change, as I know the limitations and strengths of my current kit, which is why I haven't changed before now.
I'm not going to buy a 7D2 or 5D4 until my exsisting kit no longer delivers the goods. Maybe this is an old fashioned view. But then in video land I have lots of other things to buy beyond the camera and lenses (£500 for a mic, £150 for cans, £900 for tripod, £1500 for lights, £350 for audio interface, £3500 for mac and software, £1200 for RAID) incremental upgrades push a new camera down the list when what I have is working fine.