This is basically the same idea as another idea posted here regarding autoresponding to channel comments and private messages, but with the addition of responding to video comments as well.

Here's the description from the other idea, which is phrased very well:

We get 100's of channel comments and private mail each day. We would love a auto repsonder that would send P messages of our choosing (have more then one availble) To respond when someone makes a channel comment. For Example: " Hey thanks for stopping by our channel"