Expose more of the visio object model to VBA, and provide full VBA help documentation
In a prior role, I used VBA to automate Visio- things like adjusting the shapes, overlaying external color-coded shapes on org charts to illustrate aspects of the work, etc. In more recent versions of Visio, I think there is a lot more going on (maybe to make it more functional for a variety of other user needs), but it has become more difficult (at least for me) to understand the object model, and often I have to go to other experts because tribal knowledge has replaced comprehensive documentation.
Perhaps embedded in this suggestion is a review of the nomenclature for the object model, to identify ways to make it more intuitive.
For example, I used to be able to take the classic org chart and easily change the org chart box size, line formats, text font and size, etc. More recently with Visio 2016, it took me reaching out to others to even figure out how to convert to the 'classic' view without pictures or fancy boxes, much less being able to make the changes I needed.