I guess the price bitcoin will never be stable if bitcoin still has a relationship with the market, because bitcoin will become a tool that has a price. bitcoin prices also in the set of users, such as the current bitcoin prices stable at $ 390-400 but maybe later it will change again over time
As you said it depends upon market condition and this is the main reason. It would not become stable because market always faces ups and downs and it is obvious that bitcoins also vary with it. Due to its variable price many traders are in profit by buying it at low price and sell it at higher prices.
And i think bitcoin will never be stable is just like other currency or product market that never been stable in long time..
If bitcoin will become fiat i think it will be stable but i think its impossible..