So, in case anyone is still interested, Henle did officially announce the iOS version of their app (
www.henle-library.com). Based on their tutorials, it appears to be a little bit of a glorified PDF reader that can do a few other things:
1. Add custom hand-written annotations (nothing new)
2. Add/Remove a limited set of music symbols/fingering numerals (another type of annotation) which stay attached to the staff.
3. In-app metronome
4. Basic score layout adjustment. This is what I think most people were most curious about. They have an "original layout" setting and a "custom layout" setting. The layout may be customized in two ways: zoom in/out and change system-system-spacing. From what I can tell in the video, the app isolates individual systems (and their attached annotations). If a system starts to get pushed beyond the bottom margin, it moves that system to the next page. If the spacing is changed to be small enough that the next system can fill in the space, it fills in the empty space at the bottom of the page. All notation elements remain fixed relative to their staff/system. In other words, there is no-flowing of measures when you zoom in and out, just re-flowing of entire systems.
Anyway, just thought I'd share my observations. It looks cool and gives access to their library in a handy digital format, but it's really more like a fancy PDF reader. The Android version appears to be about 4 months out.
Best,
Abraham