Great finds!

Perhaps having Ni as a conscious function in itself ‘demystifies’ mysticism from its numinous quality?

I think what we're seeing with these two NiFe ll-- rabbi's is an ego and developmental focus on their Je (Fe). As we've seen with many other samples, non-standard development often means that the person's cognitive focus is on that non-first function. Yet, their cognition remains in the same hierarchy when it comes to its weight of metabolism.
So in these two rabbi's we see all the qualities of Pi precedent-focus, worldview rambling, narrativism, exhaustive understanding of global/world-context, but there is a focus on application (Je) of that knowledge. Inversely, the NiFe l--- development has no other outlet, so Ni is the sole conscious process and its phenomenology is given full weight.

@fayest42 - mmh, y'know the curious thing about Ni is that, for Ni-leads it's not mystical. And what I mean by that is that an Ni-lead experiences their Ni not as esoteric but as normative as anything can be. Even if they appear quite mystical to the outsider, the Ni-lead him/herself feels he is just stating a straightforward view of the world. And arguably they are. So there's a paradox in perception between the individual and the public.
But when Ni is in the polar position, for instance in SeFi's with unconscious Ni, what we see is behavioral trends such as dabbling in divination/tarot, crystals, astrology, the occult, etc. Most often the Se-leads are aware, to some degree, that their activity is mystical and they participate in it because they feel a muse calling from Ni. This is the SeFi "gypsy" shade described in the book.
~
(Oh, as far as "conscious" = "practical" goes, you may be right that I could pick a more function-neutral word since there's overlap with Je! This is more of a semantic artifact, but lemmy see if I can explain...)
So for example, Ni-leads do have more practical use of Ni in that they use it to detect and anticipate the sort of large-scale societal/worldly trends that one could only do so with years and years of accumulated datasets and historicized interweaving of those datasets. The practical application in this case is the ability for Ni to operate as a source of temperance, caution, world context, anticipation, knowledge, etc. The Ni muse, by contrast, will lack the large web to give those answers (making it less 'practical'), but it will have a much more potent numinosity.