Depending on the site design and rate, workarounds may just not be worth the hassle. I'm envisioning extremely low rates, which would also make the cost difference of different reading speeds negligible. Tiny amount for each reader, significant cumulative amount for the writer. And one could argue that more attentive readers are gaining more utility, making a higher cost fair.

Maybe irrelevant, but it occurs to me that I've never heard anyone complain that their phone bill pricing model penalizes them for being a slow talker.

It could also be a useful limiter for time sinks - e.g., no ads on Reddit, but a constant reminder: is this really how I want to be spending my time? And perhaps the content quality would be higher because posters get real rewards.