I upload my videos in 720p because I can't afford to get Lightworks pro (tho apparently hit film will work, but so far its really slow and laggy.) and that footage looks ok on my brothers 50+ inch UltraHD tv.
Obviously, you can get better footage with the 4k cameras, provided you don't have a crappy camera and do things the right way, I just don't think its necessary. When you hit a certain point, you only really notice things when pointed out.
But, I don't do a videography channel, I am sure that thatPeter McKinnon fellow would get a lot of lashback if he suddenly switched to my camera (700d) at 720p.
Depends on what you are going to do. Look at your analytics, see how many people are watching you on mobile devices. It doesn't tell you home many people watch you full screen, but I almost always watch videos in the small window. So, how often is 4k just going to be a drain on your resources?
Plenty of people would say this is wrong. But, really, am not yet a supporter of the whole 4k thing.
EDIT: Maybe your channel would benefit from a 4k camera, provided it does a better job than a 1080p camera since you do such visually orientated content.