Let's try this again.

Note the original ingredients include mustard _and_ nutmeg. Note that
the original poster stated "1/2 the usual amount of nutmeg" and why.
This is basic chemistry more-so than anything else, and about as
obvious as what happens when tarragon and black pepper are mixed in a
sauce? And why adding a dry, sweet, or worked wine makes a significant
difference to those results? (Do you even know what a 'worked' wine
is?)

So, straight pomegranate juice would turn things pretty bitter in a
hurry, and combine badly with the resinous background flavor of the
nutmeg (one assumes fresh nutmeg, of course). However, grenadine,
lightly applied does none of that, does combine aptly with the nutmeg
and does add to the color, thereby also widening the choices of wine
used in favor of some more flavorful (and dryer) whites rather than
most nearly-tasteless blushes and pink wines.

You will also note that I suggested testing it first. It really is not
for everyone, but the combination with nutmeg enhances that effect
while reducing the sometimes-overly strong resin effect. In most cases,
dry nutmeg is fit only for bad egg-nog and cheap rum.

You really don't cook much, do you?

Peter Wieck
Wyncote, PA