I have the hardbound PoE guide, and it mentions druid spiritshift forms that are attainable during adventuring, though I can't seem to find any reference to them on the forums or internet in general.  The five basic animal forms are the only ones available, correct?  Any extra information out there concerning this?  Future expansion fodder?

If memory serves it was an idea discussed at some point in development and maybe in a Kickstarter update. It was ultimately dropped because making any new spiritshift form would require a disproportionate amount of work, notably on the graphic/animation side, for a single class feature.