about the darksend open source dillema - how about this, the dev could put on darkcoin.io that the source will be made open once DRK reaches the price of $100 per coin. That would mean it's well established and known by then
There's no guarantee it will ever reach that price, especially if people don't trust it, if would make a laughing stock of darkcoin. It's possible to hire from private firms for a security audit of the code. These are professionals in their field and are probably held to NDAs.