Requires for unregistered packages

[Crown421]

During some work I found that this package appears to not work with unregistered packages as optional requirements
I used the following two lines in my __init__ funtion

@require MKL="33e6dc65-8f57-5167-99aa-e5a354878fb2" println("Test MKL")
@require LinearAlgebra="37e2e46d-f89d-539d-b4ee-838fcccc9c8e" println("Test")

and only the second message gets printed. The only difference that I can see is that LinearAlgebra is registered, whereas MKL is not.
I also tried adding a Manifest.toml to the package to no avail.

Would it be possible to make this work? Maybe go as far as enabling
macro require(pkg::Pkg.PackageSpec, expr)
which would enable fixing specific commitIDs and more?
(Pkg.PackageSpec )