I'm assuming that across all of these platforms it will be easy to estimate the value of various activity. For example, a post may be worth a lot to a small number of people, or a little to a lot of people.
Ultimately it comes down to the number of upvotes, with solve configuration to prevent gaming the system. I wonder how much configuration & control platforms would have over the distribution of coin their platform. Would the platform itself be paid?
Just musing here, I assume these are relatively open answers as it's a young project.