Before class last week, I was considering the standards for considering oneself able to dance Lindy Hop at a proficient level. When we understand these elements, we should be able to improve upon them.
Perhaps being able to do a number of swingouts in a row might be a good marker. It takes solid technique to repeat 4-8 swingouts in succession. To me, this sounds like more of a measuring stick than an actual standard.
However, it's more than just doing swingouts.
Connection: There's too much to say about connection in the time that I have. At least one should consider how much they are connecting with their partners in the most mechanical and efficient way possible. Keep in mind the pain factor: if you cannot tell whether your partner is feeling pain, you might want to take a look. That's a really great yardstick.
Timing: If the swingouts are off-timed, not keeping up with or racing ahead of the music then you've got a problem. At the most basic level, one should be able to keep those eight-counts happening every 8 counts. When one becomes more proficient, varying tempos should be no problem.
Stamina: How much can you keep up with the faster songs?
These notes are pretty general. I'm sure you can come up with more. Any ideas?