Reason for replacing mifare classic
Enciphering data using AES and moving that to a card without effective security is not enough to solve some very real security issues; including most preeminently the possibility of


returning a prepaid card to its original state, re-crediting it after use (an adversary can copy the original enciphered data, and save it for future use when the genuine card is empty)
making duplicates indistinguishable form the original (which can multiply stored value, or allow to forge duplicates of an access cards)




Update: it was suggested that the content of the card be enciphered and integrity-protected using a symmetric key derived by the reader from the tag's Unique IDentifier and a master key. This effectively prevents an adversary (not knowing the master key) from altering at will the content of a card, or copying the content of a card to another card with different UID. It however gives no protection at all against attack 1 (which copies the original enciphered and integrity-protected data back to the original card); and only blocks attack 2 if an adversary has some difficulty making a duplicate card with the same UID as the original.



Note: Mifare Classic cards do not use a micro-controller, much less a 32-bit micro-controller (as I wrongly thought the question suggested), which are currently used in rather high-end Smart Cards; many Smart Cards ICs used in mobile phones SIMs, bank cards, transport cards, identity documents.. still use an 8-bit CPU, or 16-bit evolved from 8-bit, like these or these.