I also don't like reading long texts on a desktop screen but I think you're limiting the user too much by choosing a mobile-only approach. You're already defining what users will or will not like without running further tests, and it doesn't seem a good design practice. And thoigh you're talking to writers and publishers, it's about the app, and they're not common users.
Althought creating a desktop version for the novels section will demand effort, resources and time, I still think it's worth it, because you won't be limiting the user experience so much. What if I or someone else decide to read a chapter on desktop out of sheer excitement because of a great expectation built around that specific part of the story? We won't be able to.
From what I'm seeing, you're talking to lead users (writers and publishers - early adopters would be included too, if you talked to them) to make a list of user needs but you're forgetting to ask normal users about this (those that aren't lead users but will use the app frequently). I know that, on the other hand, this is supposed to be an innovative product, and it includes surprise and exclusivity. Talking to everyone about the purpose of the app and its user needs will end up sharing the concept information, thus risking info leaking and losing the surprise aspect.
But do not forget user satisfaction. You need to analyse user needs for the app, but you also need to analyse it for the desktop version, specially to conclude if it is necessary to build it or not.
I know you have talented designers on the team and for sure they have more knowledge than me, but this is only my suggestion as a design student; please don't take me wrong.
By the way, as Tapastic is updating some things, would you consider sepparating notifications content between notifications for the user's webcomics (such as subscriptions, likes and comments) and notification for the comics (page updates), creators the user follows ("[creator] shared a post with subscribers") and replies to personal messages?
They're currently all at the same tab and sometimes it's a pain to dig through specific notifications (about the very own user's comics, for example).