All Canon EF mount lenses will be obsolete (and I write this owning 100+x EF mount lenses), if Canon wants to compete with the mirrorless A7 and future A9 series of Sony by using a new mount (or never release any pro mirrorless camera).
I bought the 1DX2, and my last DSLR I will ever buy is one 5D4 for nostalgic reasons. But working with the advantages of mirrorless cameras, I can clearly see that DSLRs are a dead system in the future with too many workflow handicaps.
I really hope that Canon does find a solution for pro large sensor camers with the existing EF mount, so all the lenses still can be used. Nobody needs a third Canon mount.
Canon also needs to understand that the relaxed, decade-long domination of the pro market together with Nikon is over and they need to react faster. Once Sony comes out with an A9 at Photokina that includes all missing features of DSLRs, there are hardly any reasons to buy more Canon products.