Which is why I suggested two types of Masternodes. The standard Masternode, which I'm sure most people would opt for, and the mixer Masternodes which would receive an extra reward for the added risk of leaving the wallet open.

When instant transactions become a reality it will be possible to close wallets after a much shorter period of time of anonymisation. If people don't have any incentive to leave their wallet unlocked and even a disincentive to be constantly anonymising funds (Darksend fees), why would anyone be doing it all the time?

The bot mixers you suggested I think potenitally has merit too if itcould be done it way that doesn't reveal the identity of the non-bot mixer. I suppose they would need to be crowdfunded too.