It's *THE* perfect backup body for people like me.I won't even consider it as a downgrade!
Great compliment to the 1 series bodies.
Wasn't too keen on paying 1k+ extra for the 5d3.
different strokes for different folks.
since you already have the 1DX, it will be natural for you to look out for a low cost + lightweight FF to complement your primary body and that budget FF is the 6D.
of cause' if one has the money, he/she can go for the 5DMK3 as a secondary body too.
on the other hand, there will be those people(me inclusive) who can only afford a single FF body and this body must perform to certain expectations.
5D body with 1DX's AF, precisely why i bought the 5DMK3.