Is it possible to identify new PoW minted coins so exchanges/businesses/wallets reject them until they have definitely cooled down?
That's already done at the protocol level. 
I understand if they don't move after minting until it's confirmed PoS won't orphan them, getting orphaned would be just an issue of PoW mining efficiency. Is that correct?
The problem is not block orphaning, but reversing of transactions (double-spending).