MDI is also available in the Olive Bible Study app, and has been as far back as I can remember, even on old iPads. You can open two Bibles at once (such as Bibles in two languages, or an old and a contemporary translation) and adjust the height of the window for each of the two versions. Yes, it would be more convenient to have this inside one Marvin instance, but I'm also fine with the current solution of 2 Marvin instances.
(But, it might currently be inconvenient for certain annotation purposes – if you annotate a book in both Marvin instances, there should be a way to automatically collate and consolidate annotations from both Marvin instances, so that all annotations then appear in that book in both Marvin instances. In other words, not just device-to-device automatic syncing of annotations is required, but even Marvin-to-Marvin syncing of annotations on a single device...)
