Canon don't need an answer as it's a hack. They will simply state that the 5D III was not designed to be used in that way, wether it can or not. It's like modifiying a car engine to go faster. The car manufacturer doesn't have to answer to those mods so why does Canon? I bet you could make a 5D III do all sorts of things if you really tried!
I do wonder about their higher end video cameras though. Though doesn't this hack only let you record for a short period of time? Most working pros wouldn't really care for that would they? I hardly see the BBC (or whoever uses that expensive stuff) going out to buy a bunch of 5D IIIs for their film crew and then hacking them with ML.
Someone also mentioned ergonomics in a similar post. Plenty of reasons Canon won't be bothered much by this. They'll sell more 5D 3 and maybe one or two less C100s. End of the day they'll still be making bank and laugh about their profits!
+1, well put. I think plenty of people will ignore this hack and carry on with cameras that are designed for video, even if the Mark III produces better images it doesn't mean the others produce bad images. Everyone I know is in love with the C300, and it's ergonomics/video features make it much more appealing to documentary/run and gun people. I think major productions will ignore it for the most part, I mean the GH2 shot incredible looking video but you only really see lower-budget productions using it.
The hack is still in it's infancy, just a couple weeks ago they were saying they weren't sure they'd be able to get it to record continuously, that changed quick. This isn't even an alpha build, it's just experimental, but I think once they get this to work with an external recorder it could be really awesome.
As for the 5D3 ergonomics, people have spent lots of money making rigs and making DSLR's feel like video cameras, there are plenty of solutions out there for that.