Consider for instance the following sentence:
The obvious context is that someone has been warned about ill behavior of his new friend by others but wants to make up his own mind.
The obvious implicit subject here is the speaker. However, the way I see it, both:
Significantly alter the nuance of the sentence. The former would force the second topic to become contrastive, and a non-topical subject in this context has an entirely different nuance.
At least, I often see this pattern where a sentence seemingly “cheats” the rule of not allowing for more than one non-contrastive topic by making the second one implicit, almost as if Japanese actually allows multiple non-contrastive topics just fine, but not multiple explicit ones.
The only way I see to introduce it is with particle dropping:
Which “traditional grammar” teaches is not appropriate in formal contexts, though common informally and is “technically” a grammatical mistake. But, I've actually seen particle dropping in this context specifically multiple times in sentences that otherwise eschewed informal grammar, suggesting that it is indeed the only way.
So what's going on here? Is it actually not possible in sentences such as this to introduce an explicit subject while keeping the nuance without resorting to particle dropping, or is my understanding wrong and does “私はミコトがどんな子かは自分で見定める。” not force the second 〜は to become contrastive? And if so, does this only applies to less common “〜かは” situations or also to say “その英語は好きじゃない。” vs “私はその映画は好きじゃない。” when someone is talking about a particular film.