I just got a chance to try this. It is fantastic!
To be honest, when you mentioned the photo tagging, it didn't really pique my interest because of the difficulty in making the photo tags available to other viewers. (Now I see that by saving the photo coordinates in a comment on the photo page you may even be on the path to solving that.)
I love the other two features. Easy searching of Watchlists is something we have always meant to add. But we have never gotten around to it, and if we had, it would not have been done this well.
Same story with collapsible descendant lists. We have had in mind to do that, but I'm sorry to say we never have. You have done it very well, and it's an even more useful feature than I expected it to be. Bravo!
I'm keen to hear about your long-term plans. I think I'll message you privately and/or on the WT_Apps e-mail list.