I came to the same conclusion and I did ask ages ago :( .
Moreover, while it might be possible to reverse-engineer, from the Python files provided, how things can be done, I would need to provide menus etc to "my" users to make the extensions usable for them. I seem to remember that I found that there are some files that define the menus and hence might be extended accordingly, but I don't suppose this is decently possible without any instruction.
Being able to do Python extensions, for me is the only reason to convert my users from TP7 to a new version, which would be a major task regarding the completely full and hence not easily convertible database, the multiple scripts and Web gallery creating files an not really foreseen differences in usage (e.g. managing annotations).
-Michael