The Darkwallet concept already does work and is being used right now. Go ahead and download it and start testing it in the testnet:
https://darkwallet.is
Darkwallet is open source so anyone can audit the code, if you don't read the source yourself than you have to trust a friend just like with bitcoin core.
Yes, being in alpha , only use testnet coins, and there needs more work done. Not exactly shared send but a simplified version of coinjoin is being used. Coinjoin + stealth is pretty damn good for privacy but there are plans of strengthening the coinjoin implementation:
https://wiki.unsystem.net/en/index.php/DarkWallet/CoinMixing