I repeat:
And this still doesn't solve the issue where a masternode can simply record it's in's and out's and thus un-anonymising the transactions.
What good would only half the information do? A powerful, malicious entity could potentially purchase a large # of masternodes and try to match transactions, but no (currently public) technology would do any better in the end.
You just admitted that DRK is centralized and Masternodes are vulnerable to attack. Trustless CryptoNote protocol makes DRK tech obsolete.