Well, if it's only about the $ that can send Steemit mainstream you're right. However, I would disagree that this is what will prevent Steemit from moving in that direction. Perhaps the money brings in new users, but it's the community that keeps those that like it here.
Even then Steemit has a lot of other areas that need to be worked on for it to move beyond the look and function of a basic early 2000's social media network with limited functionality. It needs to mature faster with more focus on a dedicated development team. We need customer service to some level. Improved search, some kind of chat functionality, and a simplification of the rewards system to make it easier to get involved.
At least that's how I see it. :)
RE: Why Steemit will never be Mainstream