Why do you think that persuasive capacity is pretty limited these days?
In your example of overcoming vaccine hesitancy, it seems to me that the problem is actually that the anti-vaxxers are remarkably persuasive, considering the lack of evidence available. Likewise, most people I know tend to become quickly persuaded of the efficacy of new policy ideas introduced by politicians of their preferred political orientation, regardless of how feasible or effective these ideas may be.
I’m assuming that it is easier to be persuaded by people with whom one already agrees with than by people with whom one does not, meaning that people rarely switch between polar opposite opinions, but do still have their minds changed frequently. Do you see things differently, though?
I suspect that even if wireheading not a hard engineering problem, getting regulatory approval would be expensive. Additionally, superstimuli like sugary soft drinks and reddit are already capable of producing strong positive feelings inexpensively. For these reasons, I wonder how profitable it would be to research and commercialize wireheading technologies.
For what it’s worth, though, Neuralink seems to have made quite a bit of progress towards a similar goal of enabling amputees to control prosthetics mentally. Perhaps work by Neuralink and its competitors will lead to more work on actual wireheading in the future.