From Kristin Dos Santos of E! Online:

Ginny in New York: How about some love for Brothers & Sisters?
Gladly! I’m hearing there will be a wedding at the end of this season! But not necessarily the most traditional kind as opposed to the commitment-ceremony-ish kind. Gee, did I give away which Walker it might be? Yee!

Basically, you can take this to mean:

1) Kevin and Scotty will tie the knot in the season finale (episode 2.16).
2) Luke has signed on to be a regular for season 3, and this “ceremony” justifies keeping Luke on board (and prevents him from auditioning for other series).
3) We fans will get more Luke goodness in the season to come!!! :)