Thank you for this assessment. The book I cite, Renato Lings’ Love Lost in Translation, develops the link to Gen 49:4, but I appreciate the prompt to consider it further. And I wonder if I’ve an idea about the mystery of the plural “lyings” in Lev 18:22.
The exact problem with the Reuben-Bilah relationship is at first unclear. I’m reading Helen R. Jacobus’ 2013 paper, “Slave Wives and Transgressive Unions in Biblical and Ancient Near Eastern Laws and Literature,” especially pgs. 63–67. The problem does not seem to be just that Reuben takes a slave promised to another man (cf. Lev 19:20). The problem is also not that a son sleeps with a slave his father has also slept with, which is legal in biblical law after the father has died (cf. Lev 25:44–46).
Noting the problem is “cryptic,” Athalya Brenner (in “On Incest”) suggests the offense is Reuben being “accused of an ambition to consolidate his seniority of inheritance. Like Absolom, Reuben acted too hastily and and before his father’s demise, thus forfeiting his birthright as successor.”
This seems right. Reuben sleeps with Bilah to cut the father off from producing more sons. It is a companion narrative with Absolom. If the concubines are taken by the son before the father is dead it is an act to unseat the father, essentially to kill him.
The “lyings” of Gen 49:4, we might infer, refer to the plurality of the father’s reproductive choices, here two women, Rachel and Bilah, the wife and her slave-surrogate. The meaning of Lev 18:22 might then shift, unexpectedly, to a prohibition on a concubine taking a new man?
Now I do believe that Jewish spirituality is primarily concerned with a prophetic discourse that sees gods as males and human communities as females. A ‘concubine’ in this discourse might be a spiritual community attached to Israel—looking now at Samaria?