The issue here is not transforming every "predicate" -p function into one returning t/nil. That's not what my patches did. And in my original answer I already said that most predicates return t/nil, but not *all*. I would contend that "predicates" not returning t/nil aren't really predicates, but that's a discussion for another day.
Most of my latest patches make the function follow its documented interface (the docstring), which shouldn't be so controversial. In fact, if some function relied on the documented t result, if was risking getting something different, often in obscure cases. So I'd say this patch will help uncover bugs. (I'd be surprised that a function, for example, documented as "return t", returning a marker in *some* cases, is being used purposely so by the client code.)
In other cases, they fix problems; either because the docstring says that it returns t, but in fact they return a useful non-nil value, or because the functions say non-nil/nil, but are in fact functions that, but it's very nature, will always return only t/nil. That shouldn't be controversial, either.
I mean, if some specific change in my patches is a mistake, let's discuss it or fix it. But mostly, what I've done is fixing latent bugs, either in the documentation or the code.