From what i could understand, even by using a VPN, it's not possible to use the app from one of the restricted regions.
The extension becomes more powerful to detect the ip from the operating system of your device. This proves that MetaMask wasn't a decentralized app since its lunch and that it can be controlled by a centralized power.
Till now, it's not yet clear which regions are banned from using the app and for what reasons, as Russian users seems to be not in the list of the restricted countries. However we can find Iran and Syria as well, and this was confirmed by users from my local board who live in Syria.
When using a VPN, and a site like ipleak.net can't tell the real ip, then MetaMask doesn't know it too. Perhaps it sends data about language setting of operating system or browser to the server that has the node. Or worse, the node could have a blacklist of Eth addresses that have been used from these regions in the past. Or proxyban, then only some VPN should be affected.