What I think is this: There is a great possibility that as you said to see an ALT coin rally if Bitcoin ETF gets rejected. BUT... if it is approved, then BTC will start a new rally and will drag all the altcoins to new highs aswell(since we all know that alts are following BTC'c path) So the way I see it, ALTs that have some real value will be the real winners! Big investors are just patiently waiting...