I though that most US cities have major budget deficits,so they are relying on financial aids from the federal government.
Investing public funds is supposed to be heavily regulated and under the strict control of some government agency,so I don't think that any government will allow the investment of public funds into some digital financial asset,that is still considered very "exotic" and "risky".
To make it simpler thing of it like this, lets say you take out a mortgage, and you pay 1000 dollars a month for it, if you earn your salary and pay that off, that is good enough and whatever you do with the rest isn't anyone's problem. Same goes for this as well, you can have a deficit, you can even grow that deficit to be bigger as well, but as long as you get taxes you can put some of that into bitcoin if you want to.