This is my first post here, so please don't be harsh with me.
I have not used Band in a Box in about ten years. I just purchased the 2013 Mac version.
There are some things about it that I find disappointing.

I know that I'm making some broad, sweeping comments that talk about things that would be very difficult to implement in BiaB. I am just making suggestions here.

First, BiaB 2013 makes music that sounds a great deal better than the version I worked with ten years ago. RealTracks is a huge innovation. BiaB is an astonishingly good and rich and powerful product for what it does, and I am going to use it and get a lot out of it.

However, BiaB 2013 has the same cluttered and awkward user interface that it had the last time I saw it ten years ago. It has the same ugly and incredibly dense and complicated button bar, and the same crowded dialog boxes that use lots of plain text in a mono-spaced font, displaying the contents of text files in a very awkward layout. But a larger problem is that BiaB does not conform to the conventions of the user interfaces that people expect in 2013. Visually and in the user interface it looks neither like a modern Mac OS X 10.8 program nor like a modern Windows 8 program, and doesn't behave like either. You may think this is only cosmetic, but for a new user coming to Band in a Box for the first time today, all this is a big turn-off. Although people who have been using BiaB for fifteen years don't notice anything amiss, beginners don't respond well to something that is so awkward in its presentation.

Eventually you are going to want to make an iOS/ iPad version of BiaB, and when you do, I imagine that's when you'll get serious about streamlining and revamping the user interface, because you'll have to conform to Apple's iOS developer and useability guidelines, not to mention something that is operated by touch and not by a mouse. None of the developers I know are thrilled about everything you have to do to conform on that platform, but it's inevitable.

Second, I'm not impressed with the notation view and features. It seems to me that you have not taken into account what the rest of the computer music software industry has been developing in recent years. Have you examined and used recent versions of Finale or Sibelius, the industry standards? I would like to suggest that BiaB's notation capabilities and the way it displays notation should incorporate some ideas gleaned from studying those programs.

I think it's time that Band in a Box supports MusicXML, the open-standard cross-platform system for interchanging music notation files amongst different programs. Band in a Box should be able to import lead sheets and melodies that are created in Finale or Sibelius or similar programs, and then exported as MusicXML files. BiaB should be able to import a MusicXML file into a BiAB arrangement. It should also be able to output BiaB standard notation into MusicXML so that Band in a Box lead sheets and arrangements can be sent to Finale or Sibelius or one of several other professional programs for professional-quality editing and publishing.

http://www.musicxml.com