I really think that Kumasogami should be in the Neo series.
You're probably right.
But Matt Frank stopped doing Neos when he got hired by IDW, so maybe something better would be to see Kumasogami in Godzilla: Rulers of Earth.
That would depend on what creatures Toho has given them permission to do. I think Matt has put Neo on hiatus simply because of his IDW work & his commissions for Sunstone.
Possibly when he has more free time, he could return to the series.