Not needed, as ReactOS is open source, you will already be able to disable signature checks. Signature check is not part of API contract, it is part of the security model.
-uses Ubuntu+GNOME 3 GNU/Linux
-likes Free (as in freedom) and Open Source Detergents
-favors open source of Windows 10 under GPL2
It is only needed going the other way. See, if we want to test our drivers on Windows that enforces this, that is how the driver loader could help us. We would directly load the driver without verification on our end, but if we want to test Windows behavior with our drivers, we'd likely need something like this.
Windows supports a Test-signing mode, exactly for the purpose of testing drivers without having to sign them.
So really, this isn't useful to many people at all -- namely, those developing malicious drivers, and those who need to deploy some kind of internal tooling across their organization but don't want to put every machine in test-signing mode (and don't want to pay for a certificate). And for the latter group it's not a good solution either, because it decreases the system's security (and likely, stability).