Well, adding boars isn't a horrible idea, I could see a few additions here and there. Honestly I don't really see a big issue with adding a few more animals, that was another thing I was going to tweak anyway in the final/polishing stages (which would include unit optimizations, addition of music, etc.).
I just don't want it to get too out of hand, like if we start adding Llamas and Kangaroos and stuff like that.
I'm not entirely sure exactly where the python is for the animals, but if you have a good code editor (I use Scintilla Text Editor, or SciTE) just search for ANIMAL_DEER or something like that and it should point you in the right direction.
Since this mod is going to be the "last version," i.e. I won't be making a Diplomacy III, I plan on having some fun module packs, which may include stuff like extra animals and stuff like that. So if you had planned on doing something more involved maybe save it for that. I don't have a problem with adding boars or hyenas though. But if it goes significantly beyond that I might have an issue.