If we assume that because Final Participation (FP) is our destiny, what God wants from us at this stage of things; then perhaps it ought not to be impossibly difficult or rare. Perhaps we should expect to see Final Participation in our own lives; and in those of at least some people whose work is recoded in the public domain.
Maybe the difficulty in locating Final Participation is in recognizing it as something genuinely different and new, and therefore misclassifying it under old categories - because the old categories are all we know.
To clarify; Final Participation is an engagement with reality, in which we bring to bear our own creativity - to participate in creating.
This could be participation with divine creation (this is what I understand to happen in Heaven); or participation with another person's created work - perhaps someone from the past.
This can serve as an illustration - taking the example of JRR Tolkien's The Lord of the Rings (LotR).
Two widely known categories of engagement with life, with works; could be termed 'projection' and 'channeling' - and I will contrast these with Final Participation.
Projection is not intentionally a participation, because it describes what happens when a reader of Tolkien projects his own concerns onto the book.
This seems to be the usual practice of Tolkien mass-fandom. Except minimally; the projecting fan-reader does not experience what Tolkien himself felt or intended; but instead uses the book (selectively and distortingly) as fuel for his own interests.
For example such a fan might read LotR as-if it were a "sword and sorcery" novel, being interested only by the fights, magic, monsters, spectacle etc; and either not-noticing, skipping-over or forgetting the other material. Or, to judge by the content of one genre of fan-fictions; quite a few readers even seem to read Tolkien in a subversive fashion, as fuel for their personal sexual fantasies.
Therefor projection is not a form of 'participation' except very minimally, unconsciously, unintentionally; because the intent is to impose oneself upon the-other.
The ideal behind the form of participation I am calling channeling, is that the reader become so totally immersed in the work that he identifies completely with the author.
This is a contemplative, not creative, ideally-non-participating form of engagement - because the ideal is that the reader be passive, absorptive, and reflective. The reader seeks to lose-himself-in the work
This is, indeed, the form that has been called 'inspiration' and which used-to be (in the pre-modern era) the form that so-called 'creativity' took. The 'creator' was supposed to be a clear-channel for God/ The Gods/ The Muses - and himself to play no personal role in what emerged.
In other words; with channeling, with inspired work, the ideal is non-participation.
This channeling is therefore a particular example of what Owen Barfield termed Original Participation - which is the primal relationship with the world of the child or the early tribal Man. It does have elements of participating; but only in the secondary sense that we are then (and almost fully) engaged with the world, with life, with other beings. But (when channeling works) we are so immersed in the flow of external things, that while our own participation in them is inevitable, it is intentionally minimal.
Perhaps the ideal of the medieval sculptor working on one of the great cathedrals might serve as an illustration. He is contented to be anonymous, and forgotten, and to work in exactly the same style as every other mason - because his personal nature should 'stand-aside' and should not have anything to do with the product. I have heard of musicians (conductors and soloists) who regard their interpretations likewise: they try to identify so closely with the composer that they lose-themselves in the perormance altogether.
In terms of Tolkien, this is perhaps the ideal of the best kind of literary critic of the old school: he attempts to expound Tolkien, and not to 'interfere' by interjecting personal views or evaluations. In particular, he is very wary of 'projection', which he regards as itself a gross and unscholarly error, leading to distortions such as anachronism.
For an example of FP we need to go to Tolkien himself, in his writing of Lord of the Rings; and to that activity which he termed "subcreation".
This - I suggest - is the relationship between JRRT and his 'source material' - which came from the author's engagement with his academic subject of philology (the language-focused study of old texts), and his other concerns such as mythology, and the matter of England.
I believe that Tolkien not only had a deep immersion in his sources; but that he also went beyond immersion in his 'sources'. That is; JRRT went beyond the contemplative-passive processes of channeling, and brought his own creativity to bear on the material that he was experiencing from-within.
There are innumerable examples. Tolkien's elves are rooted in Icelandic, Norse, Anglo-Saxon, Celtic material from his philosophical studies - the words for elves, their histories, their implications (as discussed by Tom Shippey in Roots and Branches); but Tolkien also brought a deep and intense personal interest and concern with elves - which he envisaged as an ideal type of certain aspects of Men; blessed with innate health and extreme longevity, greater love of the earth, greater skills and intelligence, and magical powers.
And yet Tolkien felt a need to explain (to himself, primarily) how and why it was that elves were (more or less) estranged from, then replaced by, Men - who became rulers of this earth; despite that Men seemed inferior, overall.
To generate acceptable answers to these (and other) questions about elves, problems about myth, England and so forth; Tolkien needed to go beyond existing material and theories: he needed to enlist his own creativity.
I consider Tolkien's writing of LotR as a publicly-available example of Final Participation.
In the first place JRRT was inspired by many, already existing, source materials; and had immersed himself in these materials so that he could, when needed or desired, 'channel'/ expound/ explain these materials in their own terms, in the context of the times and places of their composition.
But in the second place Tolkien wanted to do more than just passively be-inspired-by; he wanted actively to generate something new by bringing to bear from-himself to participate with that which others had created.
This was (pretty much) what he termed subcreation.
To generalize, I think it would therefore be reasonably accurate to state that:
Final Participation = Inspiration plus Personal Creativity
As such, examples can be generated from other areas of the arts, sciences etc. The pianist Glenn Gould did not just 'channel' Bach (as some have wrongly claimed), because, although he was steeped in Bach's creative mind and intent - Gould also added his own creativity, to make something participated. A synthesis, rather than recreation.
A creative scientist of genius must, of course, build upon the valid science of his precursors; but as well as selecting from among the already-existing scientific literature that he deeply understands in its own terms (which might be said to 'inspire' him); and as well as extrapolating this work; the great scientist will bring something new, something original: from himself - in order to make a qualitative breakthrough.
In sum; I hope the above might help make clearer what is meant by Final Participation; and to help recognize when it occurs in our own lives.