You need to try margin trading at other exchanges to see how screwed is bitshares shorting. I tried shorting at poloniex last night, and now very regret that I did not try this earlier, because it makes so much more sense than shorting in BTS. At poloniex, you deposit 1 BTC, and this allows you to short 2.5 BTC worth of any assets by simply placing sell orders. When your order is filled, BTC which you got from short selling, is added to your initial deposit to back up the debt which you just created. You settle your debt by simply placing a buy order. When it is filled, your collateral is transferred to other party and your debt is settled. This is how margin trading is actually supposed to work. You deposit only 40% collateral upfront, but your position is 140% collateralized.
The guys who coded shorting in BTS clearly had no clue what are they doing. To issue bitAsset, we need to deposit a double collateral upfront, and to settle the debt we need to deposit 100% on top of double collateral. This is ridiculous and defeats the whole purpose of margin trading, which is to trade large amount with small funds. MPA is a very nice concept, which is buried under flawed implementation. Shorting is a central piece of BTS monetary system, but it is totally screwed. This has to be fixed ASAP. BTS shareholders should hire somebody who has expertise in developing trading software, pay them well through worker and let them fix shorting and all other flaws. Before this is done, don't dream about mass adoption, because other exchanges offer much cleaner products.
What a strange thread. First of all, leverage with Poloniex is based on p2p lending. Bitshares could offer this feature via a bond market, which has been proposed and discussed in the past but never implemented due to lack of consensus on whether and how it should be funded. Were you not paying attention?
Also, even if Bitshares had a bond market for leverage, that is a totally different feature than shorting on Bitshares, which is designed for the purpose of creating bitAssets. So why are you comparing "margin trading at other exchanges to...Bitshares shorting"? LOL. Obviously these are 2 completely different things, each with utterly different purposes.
Finally, in your apples to zebras comparison, you've also managed to oversimplify the process of using margin on Poloiniex. For example, you failed to mention that you have to move funds into a special margin account, where the funds will be totally segregated from your other funds. And once you have a margin position, the only way to get off margin is to close the position (and move funds back to the regular trading account if you just want to trade without margin). This is far more complicated than it needs to be. With a traditional brokerage, for example, there's no separate margin account. Simply buying more assets than you have enough fiat funds to cover (i.e. causing your collateral ratio to go below 100%) automatically puts you on margin. To get off margin, you just bring your collateral ratio back to 100% or more by simply closing some or all of any position(s), or by adding more fiat, or both.
In any event, there's one thing I kind of agree with you on. On the DEX it would be nice if your collateral ratio was calculated based on all short positions combined, not individually. That would be easier to manage. But doing it that way is not a total no-brainer because I can see how some people would prefer to manage collateral separately for each asset. I imagine users could be given the choice of managing collateral combined or separately. Another thing to consider, though, is that combined collateral would introduce some complexity when it comes to forced settlement of least collateralized positions. Although I'm sure that could be worked out.