Are you looking for a SAAS solution to spin out quick? You'd need to roll it out to see if it did keep people around and then need to keep watching your numbers as the community grew. Eventually as you get a large user base you get issues with how many people are in one "chat", moderation of offensive content, how the experience itself scales, etc. which is why larger sites may not do it (or they never found value in it)

If you're doing the startup thing though, just roll it out and see if it helps you get to a better place and keep evaluating if it's core and worth it to maintain. GoInstant has turned into Platform as a service which could maybe handle the real time component.