Anything the hedgehog might do is tricky, since it's a vermin, and thus more of an item or environmental effect than a creature.
I think main potential for changes in hedgehog (or any other vermin or "boring" animal without any apparent interesting possibilities) is connected to raws. Toady promised that new animal properties and abilities will be in raws, not hardcoded. So anything that hedgehog could do (spikes, rolling in ball, diet, lifestyle, habits, etc) can find way in more interesting animals. Imagine forgotten beast with spikes. Very deadly spikes.
Maybe this release will see better small-animal differentiation, where harmless small animals actually get a body and roam the map instead of teleporting, but can't interrupt dwarves?
Oh, this would be good. To not rape CPU more than already is, it would not use pathfinding, just move more or less radomly to next tile.
I'd think that any change to vermin would affect frame rate, at least slightly, during the function that determines what to display. I'd personally just like to see such animals be more viably utilized for their potential resources, such as meat or pelt, when trapped... it'd give a reason to actually utilize trappers on an ongoing basis.
On the topic of this thread, if I had money now I'd be pushing the boar (and domestic pig) or bobcat as a means of pushing for feral populations to be possible (where the wild form is, at least somewhat, different from the domestic one)
or for one of
the cephalopods for Forgotten Beast reasons As it sits, once I have my tax return in my hot little hands, Toady has money coming to him anyway (he deserves something for the enjoyment I've gotten from this game since 0.28.*)... hopefully something else like this will be going then too.