So not a DNA hybrid of Protoss and Zerg, but an actual entity that is composed of both a Zerg and a Protoss. Interesting take.
I like the idea, but I'm not sure I would make them the *actual Xel'Naga*, more like a race that passes as them, but ultimately, we'd discover the Xel'Naga are more akin to a mix of these designs I posted here:
Thus, the Xel'Naga that created the Temple on Shakuras and other such advanced technologies, are not the same ones that modified the Protoss and the Zerg to serve as host body and parasite. But your idea is nice, as well. Reminds me of Stargate (Goa'uld).