This is VERY small potatoes. The initial Zoetis valuation of about $2B is 1.1% of the Pfizer valuation of $180B and even should that double, it means barely a quarter a share. It's a lot to do over essentially nothing. For me, it's more of a nuisance than anything as terms for each existing options contract will change slightly once the spin-off occurs.
Its good, by keeping ZTS 80% equity, pfe can still record 80% of profits or loss from the unit as per accounting rules. Once pfe drops the equity below 80% it cannot record it on its books. So its a win win!