I can think of a few other utilities that would really benefit from a similar interface. Certain use cases of org-mode come to mind. There's nearly always a way to do what I want in org, but sometimes it's a pain to figure out even simple use cases without going to the docs or a forum. It's just something that seems to go hand in hand with all really powerful tools.
I may play around with writing a custom mode for my particular workflow of using org for literate programming. There are a bunch of commands I find useful, but don't use often enough to have committed to memory. I'd also love to be able to pull up a pop-up buffer, like magit's commit messages, whenever I want to edit a source block in more detail.
Why don't these two brilliant programmers team up and make one package twice as good, instead of working on two separate packages and mostly duplicating effort?
[1] - https://magit.vc/manual/transient/Comparison-With-Other-Pack...
Emacs ecosystem is getting really good. Org, Notmuch and Magit are fantastic for personal management.
I replaced all my custom keybindings into transient under just one C-j keybinding. Now I have a meaningful popup window with my custom keybindings, so I don't have to remember the less-frequently used bindings.
Also, transient has this one cool feature, where you can configure a timeout to delay the popup window, which is also nice.