I don't think we will be able to get smartcoins to trade at parity with the current design, which is perfectly fine because I think the current design is the best design, possibly with a few tweaks and feature adds.
I think removing forced settlement should enable prices to range around parity, just like Nubits. (Not making any comments on the rest of Nubits design, only that at least they are trying for 1:1)
First, we need to understand the roll of the short seller. The short seller is a lender that provides a service to the network by lending bts to borrowers in the form of smartcoins. Lenders do not lend money for free so they will either charge interest or charge a premium. Otherwise, the risk/reward doesn't work. For example, if I lend 1 usd into existence at a rate of 300 bts/usd with 2x collateral of 600bts, then my risk of loss is 100% of outlay (with a 50% drop in price) while my potential gains are only 50% of outlay. It just does not make sense to enter this agreement unless I charge a fee to compensate for the added risk.
Not sure I follow you here. The short gets leverage by shorting bitUSD. I'm not sure why you are explaining it in terms of the short as lender. The short actually creates a debt into the system so the short should be a borrower of 1 bitUSD in your example. The short's BTS collateral is necessary to make sure the 1 bitUSD debt is paid back in full. I assume the system adds the bitUSD buyer's BTS into the collateral pool such that both long and short have collateral for each bitUSD.
In the current design shorts put twice the collateral, but I don't think that's necessary and I assume can easily be changed. If the short only had to put 300bts in the scenario and the long had to put 300bts you would have 600bts collateral when a trade is executed (200% collateral overall). A loss of 50% of BTS against USD would trigger a black swan so to be safe the system can just trigger margin-calls at 75% of initial collateral. That's very safe esp since price feeds update every hour.
I just want to run one hypothetical example of the current system if a bitUSD trade is executed at the price feed:
Feed price is: .00345606 USD/BTS (289.3468 BTS/USD)
Collateral is 675 BTS (at 2.33x collateral against price feed) or $2.33. A bitUSD buyer would add 289.34 more BTS of collateral to purchase the bitUSD. Hence the total collateral in the system is 3.33x)
Call price is: .00259249 USD/BTS (385.7295 BTS/USD)
The shorter will be called at a 25% loss of BTS vs USD. The shorter's loss in BTS will be 96.4 BTS (385.7 BTS - 289.3 BTS) or about 14.3% of the initial collateral. The shorter will end up with 578.6 BTS (675BTS - 96.4BTS) worth $1.50.
The shorter's total loss is $0.83 (or 36%) because of the leverage instead of $0.58 (or 25%) without leverage.
If we only required the shorter to hold 1x collateral of 289.3468 BTS (or $1.00), then in the same scenario the shorter would end up with 192.9 BTS (289.3BTS - 96.4BTS) or $0.50 cents.
The total loss in that scenario is $0.50 (or 50%) because of the leverage instead of $0.25 (or 25%) without leverage.
Anyways I'm doing this late so hopefully my numbers are ok. I assume the design & collateral system works as described above. If so we should be able to reduce collateral for the shorts.