Sender A sends 4 darkcoins to receiver B.
According to the scheme you and Evan disscussed, receiver B gets 4x1DRK, each residing in a separate 'change address'.
After many similar transactions, B holds for the stake of argument 1,000 drk in his wallet, but they are scattered across 1,000 different 'change addresses'.
Suppose Receiver B now wants to have all the coins in one address for whatever reason, for example to set up a masternode. He has 1,000 coins in his wallet, but only he knows that because the blockchain sees it as 1,000 different change addresses. He therefore MUST send all his coins to a single address without using darksend even when darksend will support mixing of 1,000 coins per transaction.
Am I missing something?