Would there be a way to ai generate hour-long 4k content and automatically upload it to youtube?

Yes

And would this actually kill youtube or just force it to take action and make the experience more costly for the viewer?

You'd need an army of bots doing that and even then, you wouldn't come close to killing it, but might lead to shittier TOS in the future. YT already deals with thousands of hours of video being uploaded every minute