Would like to understand why I'd use the TAG PANE instead of inline #hastags?

You're right, the tag pane is obsolete and will probably be removed in a
future version.

It's not a good decision to remove the tag pane in the next release. My experience with tags is, that if I write a hashtag and search for this tag, I see in the result window the the text of the first line of the page. In the tag pane I have the possibility to define with the second argument the text, printed in the search result window for this tag. So this is the base of defining ToDo lists as described in the help. I use this feature also for structuring the content of the page. Removing the tag pane makes only sense, if the result window shows the text written before the hashtag. In my version 1.8.1 on Windows7 I don't see this behavior. Also it would be nice, that after selecting an entry in the search window the page view jumps direct to the line where the first instance of the tag is defined.

Thanks for the feedback. I'll make sure to cover this use case before
removing the tag pane.

One option I thought about was introducing inline subtags like
#Todo:Cleanup_Garage and display the subtags when searching for the tag.

Thank you for your answer. Subtagging is a good idea, but remember, that it doesn't allow to use spaces between the words in the subtags. The tag pane allows spaces and it allows formatting in bold, italics, understrike and so on. I think that a new solution should have the same features. Perhaps it is possible to enclose the subtag with special characters to allow the use of spaces similar the ** for formating a content in the bold style.

Good points, thank you!

An email discussion found that we need to cover the following use case:

Use case: For the To Do list, I use tags and have two categories: Tasks and Done.
Obviously, I write down all the things I have to do under Tasks and then enter
them under Done as they are completed.

Solution: Once we have "subhashtags" like #Tasks:Laundry I think your use case becomes actually easier to cover since you can just edit the text directly for each of the subhashtags. However, you will have to repeat "#Tasks:" for each task.