I believe that the #1 greatest and most powerful improvement that could be made to the FileMaker product line would be to dramatically increase the quality, the depth, and the breadth of the FileMaker Help Documentation, which is currently located at FileMaker Pro 15 Help.
I believe that the best way to do this would be to open up the FileMaker help documentation to the entire FileMaker community as a curated/edited wiki, so the entire FileMaker community can build upon this documentation and make it a TRUE resource for learning the entire FileMaker product line.
Currently, we have at least 4 problems with the help documentation:
1. Errors in the documentation.
2. Omissions in the documentation.
3. Lack of detailed examples that cover a wide variety of different scenarios.
4. Too long of a wait for FileMaker employees to update the documentation based on our feedback -- sometimes only happens when the next major release comes out.
I've only publicly posted a few of my specific issues with documentation errors & omissions, but I know that there are many more problems because I have personally sent at least 30 messages in the last year via the private documentation feedback form at: http://www.filemaker.com/company/contact/documentation_feedback.html
The wiki doesn't need to be a chaotic place... each suggested edit to the wiki can be approved by a set of trusted curators or trusted editors.
In the long haul, all of us -- together as a community -- can turn the FileMaker Pro 15 Help documentation into the greatest technical documentation that has ever existed!