The Winklevoss twins (and others) have been waiting forever!
The Winklevoss ETF was rejected by SEC on the basis that since bulk of bitcoin trading occurs in non-US markets where there is little to no regulation governing trading, no meaningful governmental market rules are in place to prevent fraudulent and manipulative acts and practices to protect investors and the public interest.
Would SEC approve a Bitcoin ETF in the future? Most probably. With China out of the equation, Japan, where Bitcoin is regulated/legalized is responsible for around 50% of trading volume, US with around 25-30% of volume and as trading volume in the US increases and other nations regulate Bitcoin, an ETF submitted by a highly centralized institution that is able to adhere with the surveillance-sharing agreements of the national securities exchange might get approved.
A Bitcoin ETF would be a game changer, horde of institutional investors would enter the Bitcoin market. Currently, in the US Bitcoin is highly regulated and as the market expands SEC would approve Bitcoin ETF to further regulate, protect investors and subsequently benefit from capital gain taxes.