I saw that a new update to FSW came out the other day, and just happened to peruse the release notes.  One of the things they mentioned is that they are working on getting the new SDK ready for the next release.  This will make it possible for third-party developers to develop add-ons to FSW.

I mainly bought FSW because I was able to get it cheap while Steam was running a sale.  I figured it was a win-win either way: if FSW ever does eventually catch on, then I got it for a bargain.  Otherwise, I'm not out a whole lot of money.