If my idea is worthless, then it strengthens the point why ECDSA is needed, and people will apreciate ECDSA more.
Your idea is not worthless and is already used in one of the altcoins. It's actually a nice solution for IoT-friendly cryptography for which ECDSA is too "heavy". The only requirements are to wait long enough between beginning and committing a transaction and to not reuse addresses (private keys).
Yep, with waiting like X confirms, for security (could be specifed by author of transaction), and removing the transaction data if private key is not revealed after X+Y confirmations, where X=Y.
Nodes could block clients that do malicious things (banlist already avalaible in bitcoin too), while the blockchain would remove unconfirmed transaction.
The TX would just be a 2 step process instead of one.
I'd imagine a private blockchain would use something like this, especially if only trusted nodes exist.