It's a sort of medievalism maybe, you know, let's make the old music sound exotic and colourful, a similar idea in Peres and Schmelzer but implemented differently. Anyway I think the book to read on this is by Daniel Leech-Wilkinson, but it's too expensive for me.
I find this general pattern really interesting. Orientalism and Medievalism, interpreting otherness in time and in space. Someone started a thread here about what you would study if you were to have a year of research. Well, I think this is a good contender.
I have the Leech-Wilkinson book on the mass, but bought it years ago when it wasn't that expensive. His book is very good for analysis of the music, maybe too technical for a non-musician, but he only gives a short biographic overview and a paragraph or two on the whole endowment/memorial aspect.
BTW, I heard back from Elizabeth Eva Leach; she replied to my email last week. She basically agreed with me that all the evidence surrounding Machaut's will, endowment, memorial concerning funding the performance of the mass after his death is circumstantial but is not "completely weak" however, she also says this "It might be that Machaut's Messe was the mass, but it might equally well be another (probably plainsong) mass." She also cites a long paper by Roger Bowers (which I downloaded from JStor).
Bowers uses different logic than Anne Robertson who argues the strongest for the mass as memorial in her book, "Guillaume de Machaut and Reims," but still considers the mass was written for a unique purpose: maybe a memorial or maybe as a gift to the cathedral upon his retirement there. It is interesting that Robertson uses a translation of the cathedral plaque which takes a few liberties with the Latin in order to strengthen her argument, whereas Bowers is more accurate acknowledging that the word "petitorium" is a legal term and hints at a legal proceeding and as a result of a less than satisfactory resolution at court for the Machaut estate, an endowment was collected by friends .
This is different from how Robertson translates the word as a "personal petition" by the Machaut brothers, and which implies a much more overt gesture by Machaut about his intentions for performance of the mass.
So, I think Schmelzer's entire hypothesis is founded on circumstantial evidence for which different conclusions can be drawn. I would have preferred had he simply said "this is how I wish to perform the music because it brings the music alive to 21st century ears" and not gone into his psuedo-intellectual explanation about the afterlife of the work.