Eventually people will want to move in and out of the ETF via exchanging bitcoin for shares which will eventually force the ETF to maintain somewhat of a hot wallet.
you cant pay bitcoins to the nasdaq! only fiat
the purpose of the EFT is to buy shares that represent 0.2btc. this is for FIAT investors to get some expereince of the bitcoin price volatility with their FIAT.
the only bitcoins entering the ETF are in basket amounts by firms that want to be fund managers annd offer shares to their clients. that are deposited to QR codes of a public key. the private key is cold stored in safety deposit boxes. there will never be a hot wallet.
by bing in the ETF trust the bitcoins are locked in and covered by the ETF's liability insurance
if the certified traders(fund managers) want to get back their bitcoins, it would be done via proper contractual communications. and the withdrawal limit is in baskets (10,000btc) in no way can someone just take out 1or 2 bitcoins. as that spoils a whole basket. again only baskets of bitcoins can be added or removed to and from the ETF.
so do not expect hotwallets and small bitcoin amounts going in and out. it all would be done behind the scenes with proper contracts and communications to legitimise the transactions.
this is not going to be a php basement dweller exchange website... we are talking NASDAQ!
and by the way swapping a real bitcoin for a share is stupid, as the share price would be slightly lower then the actual bitcoin (ETF commisions and insurance costs would dilute the price slightly meaning a $600 bitcoin would have probably a $110 share price($550/equivalence to a btc). and when cashing out you may get less then $550 after fee's, so stick with real bitcoins if you have them. and use FIAT to buy shares, atleast they will be insured if ETF gos bankrupt)