There are shops just as small as RW's that have ePub output capability: Scrivener, Nisus, even the open source Abiword. Given that it's baked into the Mac OS, it shouldn't be all that difficult. There are/were issues with the iBooks Author license, to the point where authors asked me not to use the program to create an ePub in order to avoid any legal issues. There may be a day when fixed-format ePubs can be read universally on non-Apple devices, but I don't see the advantage over pdf (just adjust the page size) or LaTeX (where, when it comes to design, you stand on the shoulders of giants). iBooks Author uses a proprietary format (*.ipa) and you have to export to ePub. This functionality wasn't in early versions of the programs, a Google search will reveal all sorts of complaints about difficulty exporting to this open source format.
Ibooks Author asks you to choose, at least initially, between a fixed format template and a flowable text template. I have no idea whether these are fungible, but if they are, why the choice?
As to InDesign for ebooks: changing page sizes in InDesign is not trivial. I can change page sizes in LaTeX by changing two variables (page width and page height). If changing paper size is difficult, I can't imagine how well InDesign would work with flowable text. Fixed layout, sure, InDesign is good at that. As long as you don't need to change the page sizes, of course.
There is a Markdown to ePub pathway. RW can give you typography, a live preview of css changes, easy insertion of graphics, even Drop Caps--and more. Is an ePub stack that bizarre a suggestion?