The biggest issue with implementing a bank feature is suiciders and countries at war.

A way to fix this would be to implement a new GDI as well as restrictions on Bank
Basicly to take loans out of the bank you would be required to join one of the GDI's

You wouldnt have to Use GDI to store cash, But storing cash as well as taking out loans would be based on networth and land.

But we would bring over the GDI from the solo servers such as express and tourney. To limit the suicider problem with taking out loans.

And make a new GDI based solely for war that way there is the option to attack since the other GDI limits it.

Each GDI can use specific parts of the bank. First GDI can take out loans while the other cant. The War GDI would be able to store more cash.

If u had a loan out in (GDI 1) and had to switch to (GDI 2) lets just say because of war, your country would "freeze" and u would have to pay the loan, or compensate what u owe with military.

With all this there is also the option of a new Bank tech, one that increases capacity of bank, interest rates ( Overall Effectiveness)

might work; i was also thinking it could be done via the alliance as a whole... but then i guess they could switch tags or something heh...

player takes 5b loan and detags and his/her former alliance needs to pay it (not easy especially if there's interest), after that stunt player would be persona non grata at everywhere.