All the 3 solutions in the post assume this. And I agree it's not the case all the time, that's why solution-c at least gives the microblogger the option to not talk about his other stuff in his microblog, if he is aware of the fact that the people following him might not be interested. Not all people who have podcasts also send a note on X.com about their latest podcast episode every time.
Discussion
I see. Well it's a solution.
I'd propose a solution d (or c.2) where the user makes these announcements in a separate kind, The follower would then have to actively query for notes of this kind to get knowledge of other stuff the microblogger wants to share.
Right now, my working solution to this problem is separate keys. People want to follow your 130 char tidbits, follow this key, they want your long form, follow another, they want your videos, that's a different key, etc. It's not too cumbersome especially if you pick one (your kind 1 publishing key for example) as your canonical identity with the information on how to follow your other stuff in your kind 0.
To me your approach seems like an elegant alternative, but I'm not enough into the weeds of that trail to give quality feedback.
After reading your article again I tend to agree. And as you pointed out the writer can choose what other stuff to talk about.
And the reader can choose to filter out too.