Tooooooo risky. Did you read the prospectus? If I was risking client money, I think I would risk their money on Somali oil reserves before this ETF.
I don't think that the ETF-specific risks will be large enough to matter. I mean, they have a large enough amount of bitcoins and it's relatively trivial to make a tracking ETF. Speculating in a volatile commodity/currency like Bitcoin is very risky per se - but if you are willing to stomach that risk, I don't think that speculating in a Bitcoin-tracking ETF would be significantly riskier.
All of this is a moot point anyway. I don't see this ever getting past the SEC.