This functionality would be useful, but you should add support for ->create(...) as well as ->get(...):

namespace PHPSTORM_META {
    override(\Magento\Framework\ObjectManagerInterface::get(0), map(['' => '@']));
    override(\Magento\Framework\ObjectManagerInterface::create(0), map(['' => '@']));
}

Would this go in your Magento project or would it be inside the plugin itself? Update: works great inside a Magento project root. Would phpstorm-library-plugin help to delegate it to any Magento project from inside plugin repo itself?

It can be provided via the plugin (which would be the optimal solution) but you can also add it manually to your project by creating a file at:
$PROJECT_ROOT/.phpstorm.meta.php/<filname of your choosing>.php
such as $PROJECT_ROOT/.phpstorm.meta.php/di-autocomplete.php