I think it will take time but it most certainly will.
Why would you answer questions at Quora if you could answer the same question at Musing and get rewarded for doing so. I think once the Quora community hear about Musing it will just be a matter of time.
In March next year there will be Smart Media tokens which will be used individually for the communities. these are backed by Steem so they will hold value. by having their own currency and identity we will see musing take off.
This token will grow each Dapps community and will allow the freedom to attract new users outside of Steemit. The new HF 20 has made it a lot easier to register new users with the account creation. Each Dapp can sign up their own users now.