I have to admit to being impressed with the way the new text features in X9 and XPLD9 are developing, illustrated well in the release notes.
However, building on that, top of my list for the next development would be the facility to be able to adjust automatic page numbering to restart at 1. Many books start with an initial section in Roman numerals, followed by the rest in Arabic numerals, restarting with 1
Close behind that would be automatic contents generation, linked to custom styles such as a chapter style or illustration style.
Oh, yes, and I wonder if the text info bar could be allowed to drop down on request to take up two lines of features?