Here's the deal - technically, it would be possible.
Here's the problem - we are worried that bulk/mass commenting across your entire channel might get flagged as a bot/spam/etc and get your account suspended.
Here's the good news - we're talked about it a lot in the past but your message just prompted me to check YouTube's API and it looks like it's possible to edit existing comments via API (before I thought we'd have to use our browser extension to edit a comment). Which means... it wouldn't look to YouTube like someone going page by page on their site making comments - if it's done via their programmatic API (that we use for a lot of things), automation is allowed and actually encouraged.
My mind is actually a little blown right now. I think we can build this feature! And I never thought we'd be able to in the past because of automation issues but w/ the API we can do it. The only thing is (which shouldn't be a problem) - that we could only *update* existing pinned comments. We wouldn't be able to automate adding new pinned comments.