count how long you are reading a post and save that locally, that would be used when issuing your upvote. The locally saved time can be easily used like some other effect of "proof of work".
I wish that can be possible, but I don't think that can effectively be done on the backend... And thr blockchain has many different front ends (steemit.com, busy.org, chainbb.com)and that would mean all of them should willingly count the time the window is left open...
If this idea can be made practically then I'd be the first to support it!!
Calling it for a challenge! =) I would be happy to propose it on utopia, but I would need some additional thinking to make it worth others spending time on it.
But I am with you, "if it can be made practical, I am the second to support it"
Good luck, if you posted it on utopia.io give me a link.