So why implement this? Just for the sake of being able to? Obviously ring signatures are desirable since Evan stated he will code them in, so why not just do this to begin with instead of Darksend?
Darksend is older technology. I'm not sure the idea of ring signatures was even around when Darksend was thought up. Also, one of the reasons Darkcoin is growing so rapidly is because people want to be Masternodes, further funding Darkcoin in the process. Had people realized this earlier, I doubt Darkcoin would have the success it's having now. To back Darkcoin up, there is a concern that ring signatures might be exploitable in the future.
If ring signatures will be an alternative choice for Darkcoin users, this directly competes against Masternode owners.
Which is why there is a growing popularity for Monero and Quazar coin. If anonymity is the objective, there are three services available now.