This was discussed a lot during the CoH's final days, and a number of articles on how NCSoft has treated the IPs of other MMOs it killed were passed around.
From recalling what I read back then, I think the most likely scenario is that City of Heroes will never again see the light of day as a commercial product. It's ultimately NCSoft's decision whether or not they want to sell off an IP: all the interested investors in the world won't make a difference if NCSoft refuses to play ball. Their worry, I think, is that an investor who gets the IP will turn it into a major success story (see: Ray Kroc and McDonald's).
For NCSoft, refusing to let City of Heroes live on is a method of preventing the rise of potential market rivals. The same could be said of many other MMOs in their graveyard.
Again, this is just the most likely scenario as I see it. There are rumors that NCSoft is going to do something with some of its dead IPs: word on the grape vine is that Exteel 2 is in development, but there has been nothing to substantiate that particular rumor.