I don't know if there has been an expansion pack announced, but I doubt it, seeing as how the game just came out.

Certainly there will be patches, but IMHO, I haven't experienced too many dire issues needing a patch, most of what I thought was buggy was me just not understanding the new game mechanics vs. RTW (for example, city wall towers, and the cavalry charge.) Perhaps the Inquisitors are a bit tough, but it hasn't prevented me from enjoying the game.