1. replace the tag list window with a pop-up list
2. provide auto-complete function base on the tag database
1. If you don't dock the tag list window, you'll see it as a popup. The only drawback is, maybe, that you need to close it after selecting a tag. The Tags plugin showed a popup, and this annoyed me pretty much so I added a dockable there as well, and if the dockable there is open, it uses it instead of the popup.
2. I think that in most cases, auto-complete that is not context sensitive will be useless - it will provide too many completion tags that are irrelevant for the current context.