ETF will be a gate for institutional capital to invest in bitcoin. If we think, who is buying BTC now?
Most money managers can't invest in Bitcoin because it is not registered security and they can't touch it because of that.
With ETF in play it will be possible for institutional money to flow into bitcoin. People will realize that Bitcoin is now backed by legal financial institution.
So BTC will no longer be 'that thing used to buy illegal goods' but instead become something approved by SEC.
All that will make bitcoin price more stable, because volatility will vaporize, and effect on price will be significant.
I quite agree with your take that Bitcoin ETFs would attract more institutional investors to Bitcoin, but to have Bitcoin backed by legal works is going to be a tall order, because the authorities are mindful of the fact that Bitcoin stands to push especially the local currencies to the background if given legal backing and for that, it should be understandable why they would rather look the other way. Nevertheless, ETFs would provide an avenue for the authorities to influence the price of Bitcoin and I think they would be interested in that!