OK so i just asked about every Japanese women im friends with and could reach this late in the day to inquire about this since i have never in my life have heard of this so called phenomenon After listening to what they said it sounds like someone is pulling your leg man or at least this is the biggest case of misinformation i have heard this week.
From what i got lots of Japanese women tend to find foreign babies even mixed ones from different cultures cute but seems to be the extent of it. One of my friends stated that basically all Japanese babies look the same LOL which i find funny since some westerners say all Asians look alike. So it would not usual for some to look at babies from difficult cultures with interest and this they are cute kind of like looking at a new puppy
but thats where it stops. Committing marriage suicide by getting pregnant and becoming a single mother is not in their best interest and being ostracized by the community is not favorable either.
So basically this is rubbish i know 2 single Japanese mothers but they live in the US and none them have any urge to return to Japan and even they said this a myth.