I love the counterparty project but I think Overstock and others went for colored coin because
4) Nasdaq will use Open Assets
My very best guess: the news about Nasdaq and Overstock might be connected.
I tend to believe it makes sense to use a colored coins like system for plain settlement, due to the much lower overhead, compared to global consensus systems such as XCP. It's clear that this comes with significant limitations though.
I think they want to rush to beat NASDAQ to market. They also inferred.previously they would start with vanilla bitcoin then move to other sidechains and alt ledgers as t his first bond issuance is just a subset of Medici (bridge them across I suppose). No idea whether this has since changed though, I don't place a lot of faith in their abilities to make honest and accurate forward looking statements.