As per this discussion I learned it is not possible in Monero to count the total unspent transaction outputs (UTXOs) in the blockchain to verify the total coin supply. I can understand that this is not even needed since the total coin supply can be verified during coin creation but I have something else on my mind.
I think of a possible blockchain application where I need to be able to destroy the oldest unspent coins in given intervals but I would like the best coin privacy possible. This means I need to be able to identify the oldest unspent transaction outputs. Could this be implemented somehow on top of current Monero privacy level?
I am afraid that what I need goes against the transaction untraceability/unlinkability of Monero because to see if an output was spend or not I need to see whether a given address is an input for transaction later in the blockchain. I just need to verify whether this is true.