This seems pretty clear to me:

    If the licensing terms aren't suitable for you (for
    example, you're developing a closed-source commercial
    product or a compiler run-time system) you can easily
    license the MPS under different terms from Ravenbrook.
    Please write to us <mps-questions@ravenbrook.com> for
    more information.

(And you can see from the exception that we got for OpenDylan that such things are possible.)