There was an attempt to create a Bitcoin ETF that was rejected by the SEC:

https://www.nytimes.com/2017/03/10/business/dealbook/winkelv...

I don't know whether the SEC's reasons for rejecting it would apply to other proposed cryptocurrency ETFs or not.

Not really. It's still too hard to do from both a regulatory and technical standpoint. There is enough liquidity and infrastructure around BTC to be feasible, but the regulators squashed that idea.

Also ETFs are great, but they are not a panacea for every asset class. Sometimes there are fundamental reasons why they don't work, but the idea is so buzzy that you can make a buck off selling garbage and calling it an ETF. Reminds me of something...

Yes, and it is itself a crypto coin:

https://www.iconomi.net/

There's an index some where in the stock market for the top 5 or top 10