In BitShares 2, shorters dont pay interest for shorting. It was kind of arbitrary and gave the longs even more of an advantage.
Instead we are moving to the much better solution of the Bond market, i.e. p2p lending. Anyone can lend their assets (including BTS) for an interest rate and collateral they choose.
No idea on the bond market's ETA. Its the most eagerly anticipated feature around here, but it seems to have been shelved for now in favour of MAS.