Can "Digital Signature of the Block by the Miner" be used in place of "Nonce"? As it is understood that arriving nonce is very resource intensive, whether "Digital Signature of the Block by the Miner" can be considered in place of "Nonce"? Its Shortcomings, if not suitable.
This only raises the question of which miners' signatures are considered acceptable.  If anyone can be a miner and provide a signature, then there is no security and no way to objectively determine which of many conflicting blocks is authoritative.  If there is a fixed list of authorized public keys, then the currency is no longer decentralized.