Sony are definately leading the pack with sensors and currently supply Nikon, Pentax, Olympus, Hasselblad, Phase One and even Canon for their high end compact model. Canon is over-due launching their next-gen sensor tech and maybe this will be it but going it alone is expensive.
50MP low noise I dont think will be the challenge the processors now & the level of software are better able to deal with this than previous sensor tech. 50MP though may show up more weaknesses in older lenses which is why Canon are working on so many new lenses.
50MP 4K in full-frame will make an awsome video camera so expect the Cinema side to benefit if this rumor is true.
You want a 5D4 and maybe 2 50 mp cameras coming from Canon and Canon wants them all to compete against each other? you know thats not going to happen,