I think the way to answer the question is: “given the distribution of equilibria we expect following this change, what are the expected costs and benefits, and how does that compare with the costs and benefits under the current equilibrium?” (as well as considering strategic heuristics like avoiding irreversible actions and unilateralist action.)
I don’t update much on your comment since it feels like it’s just pointing out a bunch of costs under a particular new equilibrium, without engaging enough with how likely this is or what the benefits would be. 
-If Julia Wise were prioritising paid emails in her role regarding community health, is she more likely to miss emails from people on the periphery of EA or who have less money, who are potentially very vulnerable?
Here, by assumption, Julia Wise already gets so many emails that she misses some/has to prioritise. So the question is: what gets prioritised currently, and would get prioritised under the new system? There would likely be a shift towards people with more money being more able to get their issues heard—but I’d expect it to be very small (e.g. initial email costs of $5-$25 might be enough). It might also allow her to find out about stuff she otherwise wouldn’t (“I don’t know if this is worth your time, though it might be, and if it wasn’t, here’s $10 to offset the attention cost”).
Though to be clear, I’ve not thought a lot about community health matters, and it’s not the area where I would pilot this.
 To be clear, I’m not claiming you should do the entire analysis, this would be an isolated demand for rigor. Just to engage more with opposing points and say why they’re not convincing.
I guess I don’t experience major problems with email (sending or receiving), so I don’t see very significant benefits. I just read your post as very costly ways to achieve marginal gains.