Yes そんなの人 is not grammatical.. that's exactly what I was talking about in http://japanese.stackexchange.com/a/5332/264 (the part on *"we can't simply chain nouns together unless to form compound nouns"*). the の in そんなの is a "noun", which means thing. Your evaluation is that the の in そんなの is an "indefinite pronoun", but in Japanese all pronouns are actually nouns, so they are actually the same thing.

Btw I've found some flaws with your original argument. If I understood correctly, you said that the “今の” in “今のは誰” is considered a synthetic noun, however.. http://japanese.stackexchange.com/q/…