So you want to start a regular credit union, adhering to all regulations. Ok. Will take up to 5 years for approval and require at least a few million in capital but can be done. Will also require substantial investment into secure banking software, ATM hardware and software, transport security, or payment into an existing ATM network you can use. You can only do transactions in fiat, so you're just another credit union competing for business amoung the already established CUs.
Then you want to issue insured bitcoin bearer bonds as some sort of deposit scheme, since no regulations will allow you to directly accept BTC and call it a currency. (If you do, immediately lose credit union licence, unless you get fed and local governments, and regulatory organizations to change the wording of CU charters)
Maybe you want to accept BTC, then convert it instantly into fiat and use that for deposits. Then convert it to BTC when people withdraw. Violates regulations, again no CU license.
You want to do this internationally which is illegal, credit unions can only take local deposits.
You don't want to start a regular corporation with voting shares, and issue insured bonds which would cost a fraction of the price and time to set up, and basically be the same thing. You could still offer full financial services like lending, mortgages and reloadable payment cards though this would all have to be in fiat to comply with regulations of whatever country you set up shop in, and that market is already flooded, especially the mortgage broker market.
Seriously you are drawing a picture here I don't actually follow. Credit Unions will have to be established in the country that wants them -I never suggested International. Five years is wrong, I can get approvals in nine months. Banking software isn't all that complicated, I deployed Van City back in the day when I was with IBM long before they merged with the one in Alberta. Fees to attach to ATM aren't really that big a deal (look around at all the private ATM brokers) , neither are cheque clearing services/scanning etc. CC's are based on volume deals and so on. Mortgage booking would be a pass through service to Laurentian or other small small mortgage book handler in Canada, US has more choices.
BTC aren't a deposit scheme, it's like having your stock portfolio attached to your account, exercising a sale and having the fiat deposited in your account. This is legal and currently done, I do it. how it's handled and accounted for within the software framework is as an additional currency, how it's termed for the sake of accounting to the public is as an asset, or bond of sort.
I get what you're driving at even if some of what you've said is not quite accurate. I think national markets will decide if they want BTC CU's. I seriously think it may be worth the effort to flush out how it might look and work even if it's not time yet.