Hello wleister, and welcome to the forum!
A. When a new file is saved in My Documents. Pop Up a bubble above the system tray that will let you categorize the file if you click on it.
B. If you fail to do that, the next time you open tabbles it would give you a list of files saved without categorization in My documents and the option to categorize them now if you click on them.
C. Have it configurable which directories are monitored for new files. I’m sure some people would want to monitor network shares as well. But only for files that they had created(not other people).
With this feature you can:
1) auto-assign a tabble (e.g. "my beloved docs") to a certain folder (and all it’s content, including subfolder).
2) open the corrisponding tabble and do File menu > sort files by fewer tabbles.
I understand it’s not exactly what you’re asking for, but I guess it’s a decent workaround…isn’t it?