The centralized blockchain looks like an ersatz approach to crypto economy. The State-owned blockchain is utterly irrelevant to the decentralization paradigm. However, it could be better than nothing. The National central bank issuing the central crypto can probably facilitate the general adoption of the blockchain technology in the society. Everything comes to the control issue one way or another: who is to control the ones who control nodes?
The centralized crypto can play like an anti-corruption method in the State-and-Enterprise relationships. The State-induced auctions for the numerous State procurement procedures can use blockchain to eliminate (or at least to reduce) the under-table solutions and unfair damping — aka collusion between corporations and state bureaucrats. It can hardly be a silver bullet for the highly corrupted societies (CIS countries, for example), but some kind of improvement will be provided in any case.
I don’t believe that the national fiat currency could significantly support the national crypto currency holding its exchange rate high. The situation might be rather opposite — the national crypto could support the national fiat adding extra value to it. However, in such a case the State crypto should be minted in a token-like manner when everyone is able to trade such a currency at the international crypto exchanges. I suppose even the poorest State could find enough budget to hire a group of high-class crypto traders responsible for keeping the national crypto in a “good muscle tone” at exchanges, especially when the Central bank’s “financial swap” takes place :)
In any case, he centralized national crypto is a pure experiment whose consequences are hardly predictable. Nonetheless, it is worth trying as a part of the entire picture of crypto economy. IMHO