I've got a Vessel subscription. I only did it to get an advantage and claim my username and comment. Their layout freaking sucks and it's hard to navigate.
IMO.. You'll never see YouTube's poster children turn against them... aka everyone who has been featured in their big marketing campaigns: Tyler Oakley, Zoe, Bethany Mota, Michelle Phan, Ryan Higa, Vice News. If you're a BIG creator who hasn't been acknowledged by YouTube why the hell wouldn't you go for the $50 CPMs? The fans will be loyal to the creators.. they're still putting out content it's not like they've stopped or changed the quality, they just get it a little bit later than everyone else (which is totally unnoticeable).
Being in marketing/advertising I've been watching Vessel since they announced the service and they've done a pretty good job to get in front of audiences and pull big creators in. Playlist Live's biggest stage was the 'Vessel' Stage, it was promoted on Twitter.. I wouldn't be surprised if you didn't see the same thing happen at VidCon. Vessel is a pimple on YouTube though.. YouTube has Google, it's the 3rd biggest website in the world and the minimal traffic that's being pulled away from it isn't going to impact them at all. Vessel is basically Hulu or Netflix and doesn't compete in the same realm as the Tubes.