I was reading Kamphuis's The Everlasting Covenant and in the midst of his deconstruction of Kuyper, he notes the following: “Regenerated man is in contact with the [Platonic] ideal world….The regenerated man sees the idea of real things, the eternal idea, that of justification, that of the church” (24), etc. From here it is a small yet quick move to eternal justification, an eternal church. I asked some Kuyperians in a facebook group and they told me that was impossible that Kuyper would have held such. As to primary sources, Kamphuis references the following (in Dutch), Kamphuis doesn't reference any claim that Kuyper champions Plato, but in the sentence immediately preceding that sentence Kamphuis mentions "a gap between man's consciousness." Kuyper, Encyclopedia of Holy Theology II:99). That's not a smoking gun, but in this review article (I know, it's Gospel Coalition. Sorry about that), While I've read Van Til's Common Grace several times, the specifics on Kuyper's platonism escape me.