Starting with the premise that cities have historically risen where natural resources exist to support it, either directly or indirectly via trade, this project has a high risk of disaster because there are zero natural resources supporting it. Everything including water needs to be piped into it. Some water could be extracted from the air or ground but for the planned population, it won't be nearly enough. So the inhabitants will need to BE the resource that sustains the city to pay for the needed resources and food. Sure it can and will need to be grown but that itself will require lots of water which they will end up rationing, at least to the peasant class living there.
No doubt the big advantage is to be able to have complete control over those living there. No one goes in or out without being tagged and tracked.
They will need to trade services for all goods supplying the city and also for sustaining the infrastructure which will be an ongoing cost. Good luck with that. I predict they will complete a small part of it but that very few people will move in and the project will then fail.
Of course the idea is ecological but even though it's desert, there is still life there and the huge wall will still prove to be ecologically damaging, not unlike how wind farm construction is killing whales.