The rat may be a disappointment, but it might be a blessing in diskise. We've got a new lego star wars creature every year scince 2009, barring 2011. 2009 tauntaun, 2010 wampa, 2012 jabba, 2013 rancor, 2014 dewback. Even in 2011 a slight redesign of the tauntaun appeared. I, personally, didn't want this years animal to be a womp rat so the inclusion of a normal rat makes room for the new animal to be in summer 2015. I recken a bantha because disny wants people to like the OT for vii. As the bantha is the only normal sized creature left to do I think this is most likely. Or maybe they'll do a space slug to scale with the ucs falcon but, for some reason, I doubt that.
So don't be sad about the womp rat like those storm troopers obviously are!