Well, to begin with, how can you possibly have a heterodox Protestant community? I do agree though, that what we have could be tantamount to an ultra Pentecostal progression, taking elements of Christianity and Judaism, mixing them together and coming up with something unrecognizable to either.
It's heterodox because they believe all sorts of things under the same label. This concept is not alien even to the post-Vatican II Catholic Church. Heterodoxy is manifested among such (nominal) Catholics as Nancy Pelosi, or some of the Wiccan nuns in pantsuits. They sort of make their own doctrine on various dogmatic issues and still claim to be Catholic. This is, of course, incompatible with Catholicism but not with Protestant sects/cults.
Thus, although they are relatively few in number, the diversity of beliefs doesn't lack among Messianic communities. Not all so-called Messianic "Jews" believe that Jesus is God. Not all of them observe the same rituals or dietary restrictions, etc. Like most Protestant communities, the doctrine is "winged" to an individual taste.
But this heterodoxy is not limited to fringe groups only. It can be found in mainline Protestant denominations, I would say in abundance, although most Protestants will tell you they haven never really encountered anyone with far-flung beliefs among various Protestant denominations—certainly not "doctrinally significant." (Mr Rogers comes to mind).
For instance, here you have an Episcopalian site which openly doubts the divinity of Jesus. I find that "doctrinally significant."