You can't naked short bitcoins, but you can naked short paper bitcoin through debt contracts provided you are sufficiently trusted and the CFTC doesn't get in your way.

The big difference between the paper-gold market and the paper-bitcoin market (other than its nascent existence) is that Bitcoin People aren't so stupid as to believe that an ETF is a pricing metric for anything other than the ETF.
Gold people tend to still see the ETF price as a meaningful price for the physical and use it for trading.  That's why there are folks shorting the ETF and buying the physical.

Bitcoiners are just smarter and more attractive than most people.  Less likely to fall for that game.
Maybe later when there are more sheeple in the bitcoin community this will change and the sheeple will get fleeced.