Why would we genuflect at all?  This doesn't seem to jive with other times/places/situations where we must genuflect:  at the Last Gospel, in front of the Blessed Sacrament are a couple that come to mind.

I have to say, the article which I believe you gleaned this information from (?) is the most scholarly I have seen on the subject of the history and meaning of this rubric:

https://www.scribd.com/docuмent/262137402/Historia-de-La-Rubrica-de-Los-Improperios-Contra-Los-Judios#

And while I obviously agree with the author's conclusion that, "it most certainly cannot be said that we refrain from kneeling because by this act the Jєωs mocked Jesus during His sacred passion," I am surprised to learn by the same article (and your post) that this error predates Gueranger.

I am happy to have paid for this education. 

If you can PM me your name/mailing address, I am happy to send you your reward.

It looks like that link perhaps doesn't give the proper attribution to the article (but I can only see a preview of the first few pages). John Oesterreicher, "Pro Perfidis Judaeis", Theological Studies 8, no. 1 (1947). 

Blumenkranz, “Perfidia” Archivum latinitatis medii aevii 22 (1952) studies the history and meaning around "perfidia" itself in detail as well. Despite the Jєωιѕнness of the author's name, he makes the solid case that there's nothing wrong with the word in this prayer (not that anyone here is claiming otherwise, just giving a summary). There are other articles from this time period that do likewise. That the Consilium would remove this speaks to how easily they could disregard scholarship if it didn't align with their ideology.

As I said, the genuflection is present in the Roman rite for several centuries until Frankish influence in the 9th century, but persisted even into the 12th century in some places. It would make just as much sense, if not more, to omit a genuflection when praying for the conversion of the pagans. Despite the commentary around the rubric, and its "historical error" with respect to what the Scriptures say, I think it was a mistake to remove this rubric because it was clearly done for two reasons: 1) the Judaizing influence in the liturgical changes (the same Oesterreicher who in this article said, "The Church will hardly alter the words perifida Judaica" would a few years later be in support of Judaizing changes), and 2) Jungmann's near-heretical thesis of the "corruption theory of liturgical history".

 Yet the Roman rite has these subtleties that show its historical growth, and they are beautiful and should be treasured, rather than cast aside for the sake of modernist pet theories on how liturgy "should" be. Another example: no Gloria or Alleluia on Holy Innocents to reflect Rachel weeping, violet vestments for mourning, etc., but on the octave day, red festal vestments to celebrate their glory as martyrs. 1962 removes all of this, even though it is ancient.