Can't you just link to sgf-file from within epub-books?
If so, wouldn't this make your main argument (which is meant to outweigh the fact that smartgobook format isn't crossplatform) moot?
As it happens, I only discovered myself last night some of the extra benefits the SmartGo format has for the user. I got the final iPad beta version of Splendid Feast with a request to approve it before it goes off to Apple, and being all fingers and thumbs I tapped a page in the wrong place. Only after a few unexpected Xs came up did a vague memory resurface - SmartGo doesn't just let you play through games/problems (very attractively) but lets you guess the next move. In the case of problems it will also automatically then show a reply selected from the variations the author has made available.
However, I really do think users have to give more thought to the poor author. This is where SmartGo pays off. Imagine an sgf game with lots of long variations and comments. In the past this would take me hours and hours to sort out, to the extent that I would blench, dodge the work, and the book would lie fallow (Until someone like Bill Cobb came long). Now, with a couple of mouse clicks I can convert that file in a few milliseconds to formatted text with diagrams already prepared for the entire game (optionally broken down into segments) and every variation and every comment, all in the right order. I just have to weave extra text in-between and edit to suit myself.
When the diagrams are displayed, they come up at the right size (e.g. main figures are bigger than variation diagrams) with all the hidden moves (e.g. Black 6 connects, or White 12 ko) accurately listed under the diagram in a differentiating font. I can tweak to my heart's content. E.g. a variation diagram might automatically start at 1, but by just typing mn=5 I can make it start at 5. If I have some symbols A, B, C on the diagram, as a courtesy to the user I can now type hideInReplay= and these distracting symbols will be hidden when the user plays over the moves one by one. I say "now" because that's a feature that has just been added by Anders, with no work from me other than bleating about the distraction.
These are the sorts of things - and there are more - that make an author more willing to get out of bed in the mornings.
If someone comes along and offers the same facilities for Androids or whatever (plus protection, so that other publishers have safeguards), I am perfectly willing to let them publish. Anders has no exclusivity (except as an Apple product). I am also willing - indeed would be delighted - for a paper version to appear, but for that users need to put their hands in their pockets to make paper publishing viable again.
Actually, I have already been approached by other prospective publishers for all formats. I have said yes in principle every time. A deafening silence follows once they hear about the paltry sales numbers or the work needed, or they decide to spend time on real life. People worry about whether Anders or Apple may or may not retire or fall into a cider vat. At least they have stood up to be counted. The other, prospective publishers have effectively already chosen to fall under a bus without ever making their marks.
