With the 6d being a related FF version of the 70D (body layout with similar MP count but also crippled from the 5d3) means the new 6d2 should float similarly near the 80D in features and body. 80D is currently the best aps-c sensor. Here's my thoughts.
24MP - this is a good number to separate it from the 5d4. 6d/5d3 was only 20/22 so next gen 24/30 seems logical.
1st FF fully articulating screen - This makes sense to test it in real world usage before implementing in the 5D series. Has to be more than just tilt
DPAF for live view but no 4K - Sharper implementation of 120??
touchscreen - This has be be able to be disabled. There's NOTHING more annoying about the EOS m hanging from my neck than accidentally hitting the touchscreen on my clothes and moving the AF pt or jumping into other screens.
19-45 pt AF - In all honesty I don't care if it's a high count. Just give me f8 ctr dbl cross pt. All other cross & outer pts that ACTUALLY work
-3EV for ALL af pts - Ah man how awesome would this be for dark reception halls at weddings?
Dual card slots. - pretty please!!! another issue for wedding photographers. I know I know all wedding photogs should buy a 5d4 yadda yadda
Digic 7 - 1st FF w/ new chip. Might be low light king of new generation.
5-6FPS - Most likely 5 to help differentiate from the 5d4's 7FPS. Current 6d is 4.5FPS
Hybrid mirror system?? Optical w/ EV option??? 6d would be the one to 'try it out' on first. This would be the 6d2's 'innovation'
the 6d2 HAS to best the 5d3 or new buyers(upgraders included) won't buy it. That means it has to have at least 22MP, similar or better AF as well as some other tasty morsels. If they can keep it to the same release price as the original 6d at $2100 they'll sell tons! My self included. I may preorder and purchase a new camera for the first time. Canon needs customers like me, finally decided that a new camera is worth it's retail asking price. In a time where they're losing users to mirrorless they need to have a successful entry FF.