As long as the price of cryptocurrency will depend on supply and demand, the high price volatility of cryptocurrency will remain. Still think the ETF funds can solve this problem, or at least will lessen the volatility of Bitcoin. The more control of the market, the less volatility it will be, now we still don't have any rule or laws to govern this market,.
Unfortunately I don't think there is an easy way to end the volatility of bitcoin anytime soon. The ETF industry is one way to reduce the demand on owning bitcoins yourself, you can participate on the increase in bitcoins price without directly owning coins yourself. The problem is of course is going to trust the financial industry to buy synthetic bitcoins instead of real ones. For the average investor the motivation to invest in bitcoin comes at the distrust of the financial industry. When buying ETFs now we put our trust in a company and not in bitcoins itself. That is why I would expect many smaller investors to buy the coins themselves rather than any financial product on it. Also there are quite a few ETFs that need to buy the underlying bitcoins for storage, so it makes no difference for the investors to buy the coins directly or buy the ETF. To a certrain extent the volatility is part of the game as it is in the stock market.