That would be a hard fork.  Miners could create those transactions to compact the UTXO set.

One of the suggestions for reducing the UTXO set is to put a cost on holding lots of UTXOs.  If there was a limit on the total number of UTXOs (like with the blocksize), then transactions which reduce the UTXO could be free.

A miner might be allowed to add 1000 UTXOs to the output set per block.  If he has already reached his limit, he could include a transaction which spends 10 UTXOs to a single address and then include 9 transactions which increase the UTXO set by 1 each.  The 9 transactions would be fee paying, but unless he includes the first transaction, he can't include them, so he may include it for free (or lower fee).