The 5DMKIII sensor isn't good enough? Its not at the end of its life either and there is some great deals on them. If you thought the 18mp sensor is ok the 5DMKIIIs will blow you away so will the 6D. Sounds like you need to actually try them. The 5DMKIII is one of the most capable cameras on the market regardless of you thinking its a poor offering. What rubbish.
No. The 5D III sensor is not good enough. Not for me. Not in 2014. Not by a long ways. In reality, 5D III is exactly what the 5D 2 should have been ... back when that one was released: OK sensor with good AF system.
And yes, 5D III is end-of-life. Even when most of its owners don't want to recognize it. ;-) And even though Canon has not listed it as EOL or announced a successor ... yet.
As a matter of fact, currently the Nikon D750 is closest to what I would want to get ... as a DSLR. But ... I want no mirrorslapper any longer. I want a fully capable, FF-sensored, yet compact mirrorless package. And the only one currently available (Sony A7/R/S) is not it, due to a number of shortcomings that ned to be fixed first. :-)
18 MP APS-C sensor is not "fine", but even worse, of course. To me, EOS-M is just a cheap stop gap measure until I finally get my "really-right" FF MILC camera system. EOS-M simply was and is by the cheapest and most compact APS-C camera system available. I find it OK for what it is and I like the user interface - there is no menu system as good as Canon's. Plus a nice touchscreen. Except there are a lot of situations where the lack of a viewfinder really kills me.