as avikz hints with the physical ETF, expect a spike.
but to know the impact/magnitude. you need to first find the details.
unless you can look at the details of a ETF proposal to know how many coins its trust currently holds, how many shares it equates to.. to estimate how fast all them shares will get sold before the trust needs to buy another basket of btc to offer more shares... you have no way of even estimating
you just end up throwing a bunch of numbers in the air like confetti and just grabbing a random number.
it might be best for people to research
EG
take the winklevoss.. i remember years ago they had 200k coins in trust (1.2bill value today)
now imagine that of 320m americans only 32m customers of a certain investment company wanted to 10% diversify their investment
According to the research, the average retirement savings for families aged 50 to 55 is $124,831. For families aged 56 to 61, it's $163,577.
..
Americans in the early 40s have a median of just over $67,000,
lets call it 100k average .. so $10k is diversified for btc etf per person
.. thats $320,000,000,000 (320billion)
ok lets say only 1% diversified as BTC.. thats 32billion
ok so we know that if only 10% of a population (lowball)
and they only invest 1% of their funds into btc (lowball)
the amount of funds looking to buy a bitcoin ETF share is 26x more than the winkles currently have
screw it lts low ball it again. lets say its a 0.1% diversification into btc.
thats still 2.6x more demand than the winkles can offer. so the winkles will need to grab up another more than 300k coins just to meet the lowball demand of 32million retirement portfolios looking for 0.1% holding