Some GUI-related suggestions -

1. For most of us, screen real estate is no longer the constraint it once was, so Rapture should give us the option to view more of its pages simultaneously.  For example, I would like the option to see, say,  CUT 1 Modulators pages for all six elements simultaneously, or, alternatively, all seven of the Modulators pages (PITCH ... AMP) for any given Element simultaneously.  This could be done floating windows style, somewhat like the way that Absynth allows multiple pages to be open. Most of the time, I have that sense of frustration that I remember from trying to program nineties hardware synths, where the poky LCD and the scroll wheel were the only way of getting at hundreds of parameters
2. Re-scale the parameters so that they are no longer in "big" values of cents (except where that is directly relevant - i.e. pitch-related parameters).  It is confusing to be faced with some parameters that range from -40.0 to +40.0 (filter resonance depth) and others that range from -13700 to +13700 (filter cutoff depth).  Even if there is a rational reason for this, the GUI could spare us from it by allowing, say, percentages to be selected as a display option, so that all non-pitch related controls scale -100 to +100.
3. Improve the envelope drawing functionality. Am I the only person who frequently and unintentionally creates or destroys nodes by right-clicking for a (non-existent) context menu? Does re-scaling the display have to be so clumsy? etc.
4. Have a pop-up signal routing diagram available to help the user quickly visualise what is feeding into what.  NI's Massive makes a half-decent attempt at this, and it is a much simpler synth in routing terms than either Rapture or Dim Pro.  Arguably, it's not necessary if you are an experienced user, but if, like me, you switch between Dim Pro and Rapture, it is hard to remember how each is configured, especially given their similarities.

I confess that I tend not to get the best that I could out of Rapture (and Dim Pro) because I find the GUI such hard work. This is a shame, because they are both very capable synths.