1DxMK3-like EOS R full rame is out of the question for this year. The possibilities for that are close to Canon re branding itself to Nonac.
Which leaves two choices:
1. High resolution - 50 mpx, keeping the naming tradition of 5DS and familiarity;
2. EOS R Sport/WL body but with an APS-C sensor.
The tiers closest to due upgrade are 5DS and 7D.
Remember how they released 7DmkII along with the 100-400 mk2? I put my money on 7DmkIII MILC + the new 70-400 zoom. Most people are going to be hyped and GASed after the 1Dxmk3, but unable to afford it, it makes senses to me if Canon tries to fill that vacuum with a wallet-friendly spicy cropper. So, in a way, the previous 32mp. rumor makes sense (if it's crop).