I have mixed feelings on the subject. When I first perused Medium and was thinking of joining I was kind of opposed to the locked story concept. But, what got me interested in the site in the first place was Ev Williams discourse on renewing Medium’s focus on the Medium blog. Because of Medium’s mission, the site isn’t plastered with countless click ads and pop-ups like so many other sites. I do not expect to see much, if any revenue from locking stories. The incentive for me to lock a story(which I haven’t done yet, as I am new here), is in support of the platform and the members. If someone wants to dive deeper into Medium and see a plethora of musings behind the veil, the subscription fee isn’t much of a barrier. A majority of hosting fees for your own web site cost more. I want to see Medium be a success. The model hasn’t been proven, yet.