This is not currently possible and probably never will be in the foreseeable future because of the simple reason of once you send a transaction to another address, you no longer have the private keys to spend that sent BTC.
So any proposal that implements an "undo" transaction will not work out because then anybody could do chargebacks, and normal people would no longer be able to trust that untrustworthy actors have sent their BTC and won't try to take it back fraudulently.
I think this is nonsense, the original transaction will simply be ignored/overruled by the undo transaction which will be recorded in block 1,2,3,4,5 after the original transaction.
As far as I know private keys are never revealed in bitcoin... it's only used to "sign" a transaction, and therefore there is no problem, and an undo transaction can also be signed by original user, whoever it was transferred to is not the new owner, as it was rolled back/undone...
I do see one potential problem with this idea: a merchant must keep up with the blocks to see the undo transaction, if the merchant's bitcoin system would go offline it might not see the undo transaction...