I don't really see an ETF being officially approved before 2019, perhaps even 2020 or even 2021. These bureaucratic things take ages, which is why I don't really care about the ETF, I can't really take this seriously, I mean, if it's not actual bitcoins traded it's a bit of a joke to me but whatever. I cannot negate that it will have an impact on the price (a positive one).
other ETFs have taken multiple years to attain SEC approval, and that's for everyday commodities like copper. it's funny to me that so many bitcoiners thought immediate approval was ever on the table.
it's likely an ETF would impact the price positively. but there's also a remote chance that demand for ETF shares is quite low, in which case baskets of shares might be redeemed for coins which end up being dumped on the spot market.