I threw my PIZZA into the air and it stuck. So, i guess the button is working.
I assume that the Stake All Coins will stake the PIZZA along with everything else.
I have to admit, I liked having coins on hand for those rare occasions when I find myself in need of a few HIVE. For example, I needed to create a new user and HiveInvite.com was down. I sold the pizza and created the account on blocktrades. I guess there are a couple coins like BRO and DHEDGE that I could own that are available for emergencies.