... The legal status is unknown although I do know that it's not legal to run an unlicensed centralized exchange.
...and if someone bites the bullet and starts a licensed exchange, the fun's only starting -- where to find registered securities to trade???
It's not currently possible to start a licensed exchange. There aren't any laws to make it possible.
The first step is to start a lobbying effort through DATA
http://datauthority.org/ to create a new set of laws to make it possible. Otherwise the decentralized route will be the only path left to take.
I might be wrong but aren't campbx and coinbase operating legally in the us?
And I completely agree with your two solutions. We either need a fully decantralized exchange (like colored coins) where these sketchy stocks can prosper freely, or a regulated centralized exchange that would probably be more expensive but I would be willing to pay for better insurance.
I think we will end up with both. It's a Napster type situation where Napster has just shut down and we all know what happens next technologically. It's inevitable that a decentralized exchange will happen and the region lock was probably the single decision that was the impetus for it. Ukyo's decision will have a ripple effect.
The technological solution is not a long term solution, it's a bootstrapping. The technological solution will eventually be regulated and that will be the long term solution.
A centralized exchange is a legal impossibility according to the vague US laws. You can thank the lack of foresight of US politicians for that. DATA authority may be able to bring some foresight into the lawmaking process and we probably need think tanks for this space.