Unclear cost: rehashing the utxo set for every block, even if maintained in a high overhead efficient data structure is a multiplicative IO cost on running a full node. Making the initial cost cheaper is essential, but at what runtime penalty is it acceptable? is 20x acceptable? If the utxo set is constantly changing, how do people synchronize it from you? do you have to hold old versions? does a peer have to fetch it only from a single other peer?
Unclear value: starting off a utxo commitment means you have only SPV security. If you were happy with SPV security; why not run SPV in the first place and dispense with the intermediate step. The answer is that it's only SPV of the history, but where is the dividing line? When someone today says how do you know that the system's creator didn't secretly mint himself a trillion coins-- the answer is because your own node verified it wasn't so.
Unclear implications: with no incentive to not run a committed bootstrapped node, is there any reason to believe the old history would even be _available_ to someone who wanted to do a full security initialization?
(*And in Git master Bitcoin Core relays blocks and transactions, and gives full wallet functionality, minus rescan when pruned.)