you still have a few short stops such as redoing some of your own tool
handles,
but I would say the next stop is art, or more modestly - self
expression
after reaching a higher technical level, you can use fancier woods,
experiment with various tools, try longer and longer finials, thinner
vessels,
or simply enjoy form, practically ignoring purpose.
Check this, or many other sites, for examples:
http://www.woodturningdesign.com/showcase/index.shtml
way behind you,
Max