UTXOs make it hard to calculate account balance. This can be fixed by merging all UTXOs of an account into one UTXO, and forking that UTXO into one to the recipient account and the remainder to the same account, for "spending". This constraint can be baked into all transactions, which turns the ledger into an effective snapshot history of each account (chain of state), while still being as secure, predictable and light-weight, though with reduced parallelizability.
Since during each transfer affected UTXOs are "locked" (concurrent operations on them result in conflicts and all but one of such conflicting changes will be dropped, or alternatively they are locked to avoid concurrent modifications), and since in such a mechanism each account will be a single UTXO, conducting the fork (from source account) and merge (into t