Like the Tiger king my first Zoo has been shut down. Well guess what Mother Fucker lol

Zoo is a Highly tweakable deck like I have said before. Pioneer however presents a few unicorns aka unique problems. There are no fetch lands and most of our remove is gone. For this reason I think it is worth reviewing the burning bush waker approach. That last line makes it should as if Zoo has an STD or something moving on lol.

Where as in modern the problem with this take is that you are going for a creature based aggro deck going wide and staying low. This approach makes the Zoo deck weak to board wipes such as Anger of the Gods.  With the format still solidifying I do believe this is a good starting point.

a few difference right of the back is the creature count spell count and land count   

                  Modern                                Pioneer
              creature 20                            creature 26
                  spell 18.                                spell 12
                  land 18.                                  land 22
        4 free spots for tweaking      0 free spots for tweaking

Atarka's Command was bad for my Zoo deck because of the number of land I play in modern and the number of creature but in Pioneer the number for both those is much higher for this reason its worth exploring again.

For this deck to work as well as the midrange decks in pioneer I believe the key is going to be green or artifacts. The key to winning is going to be ramping as mana fixing is going to be harder without the fetch lands. Draw is the next big factor positioning blue as the next favorite color. White may be the wrong color to with green and red at the moment as Simic just seems to be the best option for a base but with out hard play testing this is all just speculation on my part