I mean, there were even Bitcoin miner on Smartphones - sure, not at all efficient, but if installed on 1 Mio. smartphones they can make some pennies at nearly no cost for the app creator - and it´s much harder to identify than a secret farming bot obviously.
I see a big difference between a native reward and an app rewarding mechanism as it has been proposed in N99 and my Powerparty concept: you choose to become part of the network and you choose when you reward, who you reward and why. If the network turns out to be flawed for some reason (massive abuse by some person) you simply switch to a fork where things are handled better. This could be done with SAFE as well, but then rewarding content would be a factor of instability rather than stability.
I personally think that users should natively have the ability to approve or flag content, however, at no cost and invisible to all users, but those who you add to your personal circle of trust. This is imho the only way to grow real experience and a network of mutual checks. I see and like your intentions, I just tend to believe that once you get money into the equation things get messy.