Does an instant settlement system (such as blockchains) eliminate the possibility for short selling? My understanding is that a short sell is possible because you can sell positions you don't have and then buy at a later point to cover your position (with the price hopefully being more favorable) to settle the trade. 

In an instant settlement system (blockchains are the obvious examples, such as Bitcoin or Ethereum) would it be possible to have perform a short sell? Is there some other means of achieving the same thing?
Imagine:


I borrow 1 bitcoin from you and agree to pay you back $(1+r)$ bitcoin in a month.
I immediately sell the bitcoin you lent me.
One month from now, I buy $(1+r)$ bitcoin and pay you back.


If I can conduct those transactions, I can short sell bitcoin.