Functionally; like skid row? Certainly, that hasn't worked out well for LA; because it literally just doesn't work. Even many homeless don't want to live in places like this, because they inevitably become extremely unsafe, because the idea that a 24/7 police presence has a significant positive impact or is even possible is a fantasy. Police become jaded overnight, like trying to mop up the ocean. No one in the public (read: voters, taxpayers) would support a place like this in their backyard, for good reason. A person pitches a tent ten blocks away; what does the city do? Forcibly move them? They're back ten blocks away the next day. Repeat.
Prison being too expensive is, to be fair, true, but a problem local to only some states, and a different problem that we should be motived to solve independent of whether its a tool in the solution of this problem.
But, beyond that, maybe my point is more generally (and contentiously) stated as: I believe homelessness should be a crime whose punishment involves the forfeiture of the person's freedom of movement and work. That's a general way of saying "prison" and that's fine, but I'm comfortable stating that governments need to think about building a (undesirable, forced) path toward finding a home for these people, and making them work to earn it.
If a homeless person walks this path, gets to their freedom, and reverts back to being homeless again; well, its a revolving door, but at least its one which rotates over a span of years instead of days, and its one that makes a good faith attempt toward rehabilitation.