That is a very cool feature! Unfortunately, I just noticed today that it doesn't transfer through on crossposts.

I definitely want the expansion to come first, and then see the expanded code on lj. Because lj doesn't know what to do with the @, and the links get lost.

So I've gone back to writing the user tag in my posts, so they get crossposted correctly.

(Where would I submit this so it gets considered as a thing to be implemented?)