Someone is bound to attack my last post and say that Judaism did not allow for eunuchs to serve as priests or to join the community of Israel. But these people haven't thought about the problem enough.
The Marcionites are repeatedly identified as having a castrated priesthood. The only "speculation" we are engaging in here is how and why the Marcionites justified this bizarre practice.
The first place to start this process is to employ another feature of the tradition - its claim that the new Israel worshipped a better god than the Creator venerated by the old Israel.
As the Marcionites "retained" OT references in their New Testament the arguments about this better God - the Father - could not have been developed in a void.
The core argument must have been that Israel only saw a lower manifestation of a more perfect divinity - something inevitably present in kabbalistic literature and the writings of the Church Fathers (see the use of the Logos in Eusebius).
In other words the Marcionites must have argued that Moses only saw an imperfect glimpse of what only arrived in full perfection with their Christ - viz Mark or "Marcion."
As I see it the gospel is the story of how perfection was delivered to Israel through Jesus' "redemption" of his beloved disciple (with all the implications of that term now manifest).
Tertullian acknowledges that Jesus was a eunuch. He also says the same about Marcion (talk about being made after the image of God). Various heretical sects stress the androgynous nature of the Father and a number of statements (now excised from our canonical gospels) which point to attainment of this angelic androgeny as the whole secret purpose of Christianity.
Do the math
Stephan Huller has had a life long interest in religion and spirituality 
dating back to conversations with his grandfather, Gaston Frank. "He said we represent one of the last descendants of the Frankist Jewish faith in the world," he muses. "I grew up thinking that our family was something like the Last of the Mohicans."