As an owner of the C300, If I had to guess, I think that canon will try to compete with the FS7 with the new c300 Mark II, and it will do that by sticking with the same sensor, bayering it out at 4k and by dropping the price into the 8-9k range. Will we see XAVC or some derivitave? probably. Will we see 10 bit. Probably. Will we see increased DR...I doubt it. I think they'll stick with the same chip, essentially collapse the C500 into the c300 range and probably clean the Fs7's clock in the process. (c300 is still the most popular doc camera out there, and with the EF lens range, canon has a huge advantage over sony in this space.)
I think the rumor of an new Alexa competitor is dead-on though. The C500 has been a dog in terms of sales, as it's DR fell short of almost all of it's competitors. I'm guessing the C300 drops in price, and the replacement for the C500 (probably a new # or name) debuts with a new chip, with alexa like DR and highlight roll off, at a substantial increase in price --think f55/red.
I personally would love to see a fixed zoom lens C series camera. small form factor, motorized zoom, Dual-pixel AF -- something that brings back the simplicity of the GL and XA cameras with a large sensor....something you can put a less experienced operator on and they can handle. I'd buy two.