I know of at least four ways we can create tradeable assets on BitShares, and I think all have their place in the future (some now):
1) Smartcoins that allow speculative trading based on feeds with no gateways in or out. These can be used for coins where gateways are difficult to implement for technical or regulatory reasons (everyone knows the regulatory challenges associated with fiat gateways, for example). If witnesses are willing to provide feeds and we have an active committee willing to approve them, we could rapidly enable smartcoin trading for any number of crypto assets. Of course, we may still be faced with the same issue finding people willing to short smartcoins into existence as we have with fiat smartcoins, but I think we might find quite a few people willing to short very speculative crypto coins. I've certainly seen a few I would short.
2) 3rd party-backed UIAs like the OPEN. assets. To support real trading, these need to have gateways associated with them, so there is additional work required to support them. They also bear the risk of the backer being robbed or even an insider embezzling the funds, so it's important we vet them before promoting them.
3) For coins with larger deposit amounts, a multi-sig backed coin can potentially offer additional security versus 2. This is technically feasible, but there's a lot more overhead in supporting these coins, so I think it's only appropriate for assets that represent substantial amounts of money. And doing the first such coin will require a lot of work to create the mechanics for it.
4) The "holy grail" is a true sidechain coin, that allows coins to move from one blockchain to another. This requires a huge amount of work, and in some cases, political agreement between the chains involved. At the current time, I only see this as being appropriate for very top tier coins in terms of trading potential (e.g. Bitcoin, Ethereum, and graphene-based blockchains at the moment).
We're doing 2) today. I think we should experiment with choosing some "hot" coins with non-standard wallet technology that makes gateway implementation a pain for 1). And once I've got some time, I would like to put development effort into 4) for btc and/or ethereum, depending on the state of things when we get there. I'd actually prefer going after 4) before 3), since I think the cost/benefit ratio favors 4).