The inclusion of 4k video in the GH4 is great if you are someone who is looking for something that specifically does exactly what the GH4 does. But if you think that this is going to impact the market in such a way that Canon will be forced to counter in the immediate future, you are lacking an understanding of big business.
Again, it should be pointed out that the goal of any company is to reach as many consumers as possible and sell as much as possible. To do this, you are appealing to the average consumer with an average understanding of the products in general. At the moment, the average consumer is not yet yearning for 4k video. This will inevitably change at some point, but not right now merely due to the fact that m43 companies are putting it into their consumer grade cameras.
Quick test, go and ask 10 random people (non photog/videographers) to define what 4k video is for you and see what you get. Then come back and tell me how impactful this development is going to be.
I think you would be hard-pressed even now to find many people that could tell you what 480, 720, and 1080 are.
Canon is not merely marketing their products based on the fact that they think there are 10 million photographers/videographers that are going to buy their products. They are marketing to the average person i.e. the soccer mom or dad that wants better than cell phone photo/video quality and are looking for a boxed kit when at Costco, Best Buy, Target and Walmart. There are plenty more of the latter type of consumer vs people like the ones on this forum that cling onto every singular development in any imaging company.
BTW, I'm pretty sure they are selling a lot more Rebels than any particular L lens which should be pretty indicative of what the market is primarily composed of.