His oeuvre is distinctly less even in quality than that of Chopin's
I'd put it as having a wider range of styles and tones, since I cannot think of a Chopin piece that does not contain rubato, have an entirely different harmonic material that differs largely from his other ones or with loads of chromatic notes running up and down.
I'd contend that his Op.39 contains the greatest wealth of riches in any single opus of the entire piano literature
While I completely agree with it being a great wealth of riches, I don't suppose anyone should dare say it is the greatest since the piano repertoire, as maestro Hamelin has said, is thousands of times vaster than we know. I understand this is totally arguable, since why would those pieces be famous if they're not of high quality? I do not think we should exclude them from considerations, however. Also, I know this might sound rude, but in the end it is a compilation of pieces, even though the keys are in fact arranged in a specific order. I can think of many compilations that are also rich in material, Liszt's S139 for a starter, which I regard as the piece that sums up Liszt's compositional character(without his "Hungarian Rhapsody side"), and Liszt's mazeppa etude being "the" antipode to the 4th mvt of the Alkan symphony. If we're talking about the solo concerto alone, especially the 1st movement, then there's no disagreement since it is one of the greatest and riches pieces of mortal music on earth (the closest to sounding godly being Rach 3, though the rich and never-being-banal part has to be sacrificed for this) counting or not the undiscovered repertoire.
A little outside the topic, I think the concerto is not played to its full limits. What Alkan was famous as a performer, except for his formidable technique and interpretations, was how he could imitate timbres of different instruments on the piano. What etude is the concerto, or the symphony, if their intent was not to train the pianist to be able to perform such an imitation?
Anyways, Alkan's greatness is not to be doubted. As an admirer I would certainly participate in this project. If my technique can be improved to the point where I can play the Waldstein before the due date, then I might do a movement of the sonatine. If not, because of exams and such, I'll do a couple of the wondrous op.65, which is by no means a lesser work than the sonatine.