I believe that musing.io will overtake quora in next few years for that musing.io needs our help to make a big platform.
Musing offers rewards for answering questions, and will definitely retain a lot more people then Quora would. Only problem is the popularity of Steemit. As Steem grows, so will Musing, and with all the drops in Steem prices recently, less people will want to stay.
It is impossible if we don't help it to grow the community and platform. Now i am not saying that its impossible. It is possible but not right now. Musing can become a true competition to Quora in the next 5 years. As crypto will keep shaping the new world with the new icos musing can overtake quora. But it would take our help too. Become an evangelist for musing on your own.
Quora has lot of questions around 15 millions and musing has just 6000 question so to overtake musing should have a time to overtake and for that we should fully concentrate on joining new user so people can ask question and also able to write answer.