Translating hyle as “polymorphy” is such a cool choice.

Emphasizes how, as Aristotle already tells us all the way back in Metaphysics Z.3, matter is not a thing (μήτε τὶ). It doesn't exist as any item that one can pick out and point to as an ingredient in the thing, and hence likewise the platonists will say that it is nameless and unknowable, just as the One is (The name “matter” is a transferral from the things standing nearest). Matter is rather precisely a way to talk about how certain things display a receptivity to multiple forms or essences, a capacity to gain and lose forms, which precisely as a receptivity can be neither objectified nor identified with any form or essence. “[and] when the soul has stripped off all that lies upon sensibles like light, it is no longer able to make what remains definite, and this is comparable to seeing in the dark,… Is it seeing, then? It sees in the way that one might see an absence of form or an absence of colour or something lacking illumination or especially something that has no magnitude. Otherwise, the soul will already be endowing it with form” (Enn. II.4.10)

Similarly this might also impel us to rethink the meaning of saying that matter “participates in unity but not in being/essence.” Since matter is not a thing (a τὶ), surely it can't be conceived as something that participates unity, or itself “possesses” a trace of unity. Instead we might see it as precisely the most minimal trace of selfhood, and therefore see receptivity and polymorphy as itself a sort of goodness rather than mere deficiency.