That is a question that the community will likely have to answer going forward, whether or not Steemit should be the aggregator. There are likely a number of paths that could be taken. Steemit could become an aggregator, while a number of sites pop up using the technology. It could end up that a number of users move to sites dedicated to specific types of content, or use multiple. It could also end up that the Steemit community eventually rejects the new content, and either automatically filters content from other sites, or allows the user to.