Yes, margin trading on GLBSE assets is very important, preferably on GLBSE itself but an external platform would work too.

No, I don't think it as straightforward as you think. If you treat it as an easy hobby project rather than a serious undertaking, I wouldn't trust the result enough to use it.

If you go ahead with this, keep in mind the following:

1. You need to take into account not only asset prices, but also dividends. If someone short-sells an asset, you need to keep track of dividends paid and deduct them from his balance, and so on.

2. Most of the assets aren't very liquid, with low depth and high volatility.

3. Many of the assets are capable of very large swings - e.g., buyback clauses of bonds which instantly cause the price to spike, pass-through bonds which can drop to 0 if their underlying defaults, or just the bond issuer defaulting. For example, it is fundamentally impossible for an untrusted party to take a leveraged long position on Pirate, because 100% backing is needed in case he defaults.