Re: consider "Like" a follow #suggestion
What about considering a "Like" to be a follow?
There was an earlier suggestion that the Message Selection controls be added to group message/topic pages, rather than be hidden away only on the global /topics and hashtag pages. Would that do what you want?
Maybe Follow (for those who are Following Only) could appear as a star next to the Like button centered on the bar below the message. Even though the follow applies to the whole topic, and I know that the /topics page uses a button at the top for this function, I dislike forcing the user to scroll to the top or some other place to find it. I would change it there too if I could. Or maybe have it both ways.
Likewise Mute could appear as a circle-slashed speaker icon in that position, for those who are All Messages.
If that's considered too brazen, or consumes too much space for mobile, I think they should at least be added to the More menu.
I think there was a years-ago concern that exposing these controls in the group's Messages/Topics would be too confusing for web-reading members, who don't directly get to see their effect. I think that could adequately addressed with tooltip text ("Follow this topic in email") or similar means.