The idea of people being more invested in your channel if they comment is the strategy I've taken for my channel. I've made my channel something more than just videos to watch. The viewer gets to influence what is uploaded. I make it very clear that I take requests and ask for people to suggest things. I then do almost every one and tell people when it will be uploaded. Because of the high volume, any requests today will be put up in early September. And this is with me uploading twice a week.
When viewers see that they can request videos, it automatically changes the channel from a little entertainment value into something they can have an impact on. And because they have requested something, they have a reason to stick around if they weren't going to before. And then when I get to their request and tell them the date it will be uploaded, usually months in the future, the only way they'll be able to see it is to subscribe or remember to check back on that date.
