That has been tried in a few places, and I'm not sure that it has succeeded anywhere. Municipal fiber was laid where I used to live in Provo, UT and it had huge funding problems. ISPs could compete, but all the value is in the last mile not in the gateway.
Eventually Google bought it out, but the city had to increase taxes to help pay for the current bond, and was looking at more bonds to pay for it before Google stepped in.