tsuwm, the definition you referenced upfront ('a bright appearance in the horizon, under the sun or moon, arising from the reflected light of those bodies from the small rippling waves on the surface of the water') doesn't seem to me to be at the same as 'moonglade', or to be what Allison was looking for.

Kumatage is brightness in the horizon, she's looking for brightness in the water, whcih could be quite some way from the horizon. I know I'm being pernickety, but I do think the two are separate effects.

This is not to say that kumatage is anything other than a charming word, although I personally prefer moonglade for its inherent poetry. Then again, I don't think moonglade quite conveys the idea of a pathway that Allison had in her first description.

No helpful words to offer myself, I'm afraid, but Broome, up on the NW coast of Australia, has a famous tourist spectacle called the 'Staircase to the Moon', which is a phrase capturing that idea of pathway at least, although decidedly unpoetic.
No pics on the official tourist website, but I did find one here:
http://www.mlb.broomeaccommodation.com.au/index.site.attractions.attraction.195.html
I also note they have a night market to help tourists 'appreciate' the sight - reminds me sadly of the Japanese stringing everything in sight with pink plastic flowers, then hanging out in loud drunken parties to help everyone appreciate cherry blossom. Maybe I am missing something in just wanting to admire nature quietly on my own rather than as a mass activity?