Seriously, this is in a way a parallel to discussing "Fontaine 1917" by Marcel Duchamp. (I'll spare you the obligatory image of the urinal)
Bonsai is an art, Chojubai is bonsai because the artist says it is bonsai. Similarly the case when Chojubai is a kusamono because the artist says it is a kusamono.
As Cadillactaste pointed out, Chojubai has appeared at Kofukuten, exhibited as bonsai, and also exhibited as Kusamono. It would be easy to compile a long list of shows where Chojubai has appeared exhibited as bonsai, and an even longer list where it has been exhibited as Kusamono. It is what the artist exhibits it as, and the "jury" of art critics (bonsai judges) has accepted it as such. The number of shows (hence a similar number of judges (the art critics) have a long track record of accepting Chojubai under what ever category the artist presents it, bonsai or kusamono. So the bonsai community does accept Chojubai.
"Purists" - I suppose this would be a narrow subset of bonsai practitioners. I know from K Murata's book, Four Seasons of Bonsai, that Murata had Chojubai in his personal collection. I can not imagine a group of "Purists" not including Murata or his descendents who are running his nursery now, to be a credible group for dictating taste in Bonsai. Who is the artist that is now caring for the Japanese Imperial Collection? Does the Japanese Imperial Collection have a Chojubai? I don't know the answers, but if the Imperial collection does contain a Chojubai, I can not see how the "Purists" could exclude Chojubai from their "list of bonsai" and be viewed as a credible group.
I can easily imagine many a bonsai artist looking at a specific specimen of Chojubai, and judging an individual as "not bonsai", though it would be "not ready to be bonsai yet", rather than there was anything inherently wrong with the genetics of cultivar.
Chojubai is not a "perfect" species for bonsai. It is slow to trunk up, developing single trunk specimens is difficult. It is not as winter hardy as the "Toyo Nishiki" types. It is not the fastest growing of Chaenomeles cultivars. But many, many artists are willing to work around these short comings. I can see one being critical of its less than ideal traits. But in my book, and it seems most others, its strengths far outweigh its weaknesses as bonsai.
Chojubai has been around as a cultivar or variety for at least a century. In early books I recall Chojubai only being used as a kusamono, but for at least the last 50 years it has made more and more frequent appearances in the role of a bonsai tree, the focal point of a display. I'm sure this shift is because material available has been maturing. A young Chojubai, is just not ready to be the focal point, but get 30 to 50 years on it, and then wow, it can really hold its own against other high quality species.
I love Chaenomeles in general. I love Azaleas. Two things about Chaenomeles that make their numbers in my collection (about 7 cultivars) higher than the number of Azalea in my collection (4 cultivars). Many cultivars of Chaenomeles are fully winter hardy in zone 5b, need no added heat over my winters. And their habit of blooming more than once a year.
I do think Chojubai is over promoted sometimes, and the other really great cultivars of Chaenomeles are often neglected. There is a nice color pallet, from white to orange to red, and multicolored. There are peach, and pink colored forms too. Some are single and some are full doubles. The contorted Chaenomeles are really cool, the dwarfs like "Hime" and "Kan Toyo" are very similar in leaf size and flower size to Chojubai, they only lack the "bark" that Chojubai develops. Though who knows, does anyone have a 50 year old "Hime"? Wonder if the bark does get rough like Chojubai? So for those that can't get or can't afford the Chojubai of their dreams right now, check out some of these other cultivars, there are some nice gems in this group, and they can be quite modestly priced.
