I honestly don't think anything similar could kill YouTube. It would have to be a whole bunch better to even make it budge. The problem is that so many people are used to YouTube, and familiarity is a brands best friend. That said only time can really rell.
Just because Amazon trademarked a name does not mean that they will actively be looking to use that name. Often companies trademark names to avoid others using the name. Some companies trademark the weirdest names and even trademark misspelled names similar to their products, just to protect themselves. Obviously that does not mean that there is no chance that they actually DO make a Youtube competitor, I just feel like it's very unlikely. For instance, why would they even want to? From what I understand Youtube is still not profitable to this day. What is in it for them, except for the same pain in the a** issues with advertisers and all that stuff that Youtube has been battling the last couple of years. Another great question: why would they launch a new platform and not just build on Twitch, which has been expanding to cooking, traveling, talkshows, crafts etc. in the last years? The example about Google+ is also a very valid one. People don't just randomly switch platforms. It takes a ton of money to get people to switch and even more to keep them on a platform. If you are going to bet your money on Amazon, you might as well just go to Twitch right now.
If Amazon do compete with YouTube then they won't be doing it as a charitable act to disgruntled YouTube creators. They will need it to make a profit, even if that takes years to accomplish.
From what little I have read about Amazon and their foray into video publishing, I think it is more likely they will have an even higher barrier to entry than YouTube, not lower.
Having said that, I think they have a huge competitive advantage for YouTubers who sell merchandise on their channels. At the moment buyers have to go from one platform to another in order to buy stuff. If Amazon creates a system that people can buy by clicking on the video then that would be very interesting. Added to that Amazon already has an incredible algorithm that monitors the buying patterns of it's visitors, so for merch-selling-YouTubers this would be very attractive indeed.
They will do it right. They will not allow you to join and monetize your content right off the bat. It will potentially be harder to get in to, and you might have to prove you are a good content creator by submitting your work to them for a review. And you can bet your behind that both YouTube and Amazon will put policies in place that content can only be shown on one platform. As soon as you try to play both sides of the coin they will cut your channel off and probably terminate your account.
YouTube will prevail. No doubts about that. The only people that are exited for it are disgruntled YouTubers. And the grand majority of those don't have any right to be disgruntled because they are no where near CLOSE to making a living on the current platform.
I feel like competition is healthy, if lets say amazon does kill it Youtube has to step up their game. Youtube has been like the only platform where video sharing reign supreme. Of course with no competition Youtube is bound to make mistake and always have to be the driving force to make new ideas on how to make the creators and themselves prosper. So personally I hope Amazon kills it! It will definitley wake Youtube up and we can go yell at Amazon for messing up!