At current prices and for my goal of having a light, hand holdable, high res rig for BIF I think I would prefer the R5 + 100-500mm + 1.4 TC as opposed to the 1DXIII
I could also see using my EF lenses with an adapter on the R5 for more static shots
I would keep my 1DX which is still a very good camera for low light.
Also would keep my 5D MKIV
My 5DS-R I would consider selling to partially offset the cost of the R5 rig
Now I only need a $7K winning lottery ticket