I'd be for that but not sure how that would work with exchanges and pools.
QT client default ON, darkcoind default OFF.
Then you wouldn't be able to say it's automatic or mandatory if there would still be an option for those to get around having to do it from the start.
I think just having DS on by default in the QT client would greatly speed the mixing process. How many regular users are going to mess about with it or run the daemon instead? Why would they? DRK is a private coin, if you don't care about privacy there's BTC.