As long as Bitcoins price is so unstable, Amazon will certainly not start accepting Bitcoin. Surely it will take a long time until we can pay with Bitcoin on Amazon. The acceptance of crypto must still grow worldwide before it can be achieved. Only when this happens and the market is big enough, Amazon will jump on the crypto train, i am pretty sure. 
Ive heared a rumor before that amazon is planning to accept bitcoin . idk if that was true or they already take actions to implement it because i didnt access their web page yet . they arent bother with price unstability because bitcoin is built this way . the price cannot be stable forever as the demand and supply will move .
What merchants are waiting is the adoption . if all people will recognize cryptos . thats the time that they wont doubt using it as their official payment gateway .