Whether it would make the market more mainstream, we do not even know. Whether, there would be more money in the market ? The market simply has been growing on its own over the years without any regulation.
I know it could usher in some growth but we really need to consider the aspect where bitcoin would not at some point get to be what it was meant to be if all these things start panning out. I may be wrong, but I see us doing better in the long run without any ETF approval.