It is highly inaccurate to use HF20 as a yardstick to measure engagement on Musing.
Steemit generally experienced low level of of interaction as most steemians were unable to post because of low RC while others waited for their RC to charge up before commencing with posting and overall engagement. Only a hand full of steemians(whales and new users) could make post and comment.
I believe people will still engage with Musing without upvote. Why? Quora did it already.
It will definitely will, but will not be as successful it was before it. However, I think that the lack of upvotes after the upgrade has lead to some sort of spam purification. Before the upgrade it was too cluttered in my opinion with all sort of nonsense and childish questions just for the upvotes and one should really scroll for a while to find anything interesting and worth answering while now when there's no upvote anymore it's all clearer and more easy to "walk through" it. I do believe that the upvotes will come again soon.
Well thats not fair to judge Musing during the HF20.
As we all know that after HF20 implementation lot of issues are being faced by users.
Although Steemit team is working on these issues.
But by the time these issues are settled completely activity on steemit and Musing will be limited.
So there should be no comparison, as lot of accounts are still experiencing problems with posting upvoting and commenting.
I think once the issues are settled the Musing engagement will be back to normal.
To be honest, I'm sure there would be a lot less activity here on Musing if no one gave any upvotes here anymore. While other places are thriving without anything getting paid, I think it would be really difficult to remove rewards after people have already gotten used to it.