Maybe I just don't understand, but what Novus Ordo priest will want to say the TLM (aren't most of them happy with the new Mass?). And even if some did want to say the TLM, they don't know Latin or the TLM so does that mean they will have to go on retreat somewhere to be taught by SSPX priests or Independent priests?
Now suppose a N.O. priest learns Latin and the TLM, will his sermons be any different than if he was offering a N.O. - just because they start celebrating the TLM, it doesn't mean that they have stopped believing in the errors of Vatican II or will suddenly start talking about the evils of certain types of sins.
As for the N.O. people who start attending the TLM, they will show up with no head veils, immodest dress, and still talk after church. I think they won't become morally better or orthodox in the faith because the problem is not just the TLM, it is what they are taught by the priests as far as how to be true Catholics. I think they will attend the TLM not because they will become traditional Catholics but because maybe the TLM is at a more convenient time or maybe they are in the mood that Sunday to attend the TLM (kind of how one day you are in the mood for an apple and the other day in the mood for an orange). I don't see this Motu Propio as making N.O. Catholics any more orthodox in the faith.