Some "experts" has made lots of wrong prediction in the past.
Fixed that for you..
The cryptocurrency market (especially bitcoin) is very irrational.
While an approved ETF might have a positive influence, i wouldn't bet on it.
Especially in times without too much of activity, it seems like the chart doesn't care about any news (neither positive nor negative).
I can very well imagine that an approved ETF would arouse some peoples curiosity, which then could lead to a rising interest again.
But i don't believe it will trigger another bull run as seen in 2017.
At least a positive movement seems to be more probable than a negative one regarding an approved ETF.