That said, Aina got a nice expac last year.
Which just proves that its not impossible to add to JimT's work, you just have to be reasonable in what you want to accomplish.
That being said, a LOT of writers that do want to and attempt to write expacs for Jim's characters tend to want to write expacs that are even more ambitious than the original works of his, which usually leads to said burnouts. I like to think that this could be avoided by not
strictly following what JimT did himself, but go off of the base idea and make a small little extension out of it.
For example, an idea I had floating around in my head (and that I've been throwing out for a while now) was for Embry, I'd like to make an expac with her that explores her amateur novel writing hobby. Steele could temporarily have her be a crew member to take her on mini-dates based on the planet they're on (Cept Zheng-Shi... she's too innocent for that!) and get some ideas for her novel through those. By the end of things, you can get a new story added to your codex written by her. Of course, some additional sex scenes could be added along the way of this as well!
I would still like to attempt this sometime if I could get my butt in gear to start writing! >.<
(Heck, I'd even do this as a commission if someone really wanted to motivate me after I finish up the last of the Kiona stuff.)