I looked through the documents you linked to, and I get a strong impression that this is an experimental design, perhaps done as a hobby or an academic exercise. I don't want to discourage experimentation in any way, but I don't think there's a real need at this point to reserve an e_machine value.
I'm open to reevaluating this if you gain support from additional toolchains and/or if there's a likelihood of building real hardware that supports this architecture.
I'm impressed, though, with the work you've done on the ISA and psABI!
-cary