since your standard is already that high, I ask you for even more
1. Lack of additional synth fx plugin versions
WHAT Additional fx plugin. You did this already in Zebra: Every of your synth plugin should provide an additional fx plugin containing the exact fx section of your synth.
WHY The synth's fx often sound pretty good and usually are designed to nicely fit to the synth's sound character. But in various mixing situation in a song context, it simply makes no sense to use it anymore due placement limitations. Examples: Multilayering multiple synth instances, very common these days. Or special stereo and panning treatments. Or external compression. etc. etc.
WHO Zebra fx lacks of preset import AFAIK. All other of your synths need a fx plugin. You could charge a small extra amount from synth owners, and a bigger amount from new customers.
WHAT Copy/paste buffer realized in human readable (text) format, cross plugin compatible. So you could copy a preset in Zebra, and then paste it to Zebra FX, or a note pad. See Melda plugins as reference, or Renoise while opened with multiple instances. Ideally the fx version also uses the exact same presets and preset directories for the saved versions.
WHY Saving the preset in the file directory structure is cumbersome. You would to have to manage the same contents multiple times. Also this would simplify a lot of other workflows.
WHO Any synth
2. Lack of layering/mixing filters/tools
WHAT Commonly you layer multiple instances of a synth these days, to overcome limitations mostly, or doing fancy stereo/doubling techniques. Most of your (and all other) synths lack of layering filters. This could be provided by other filter plugins or the DAW, but maybe you know best what sounds best. Also you could provide here key following filters. Also layered instances could cross communicate to provide parameters like "collection detuning", so once a parameter was connected thru the layered instances, the parameter could spread in an intelligent way, etc.
WHY Ease of use. Better sound.
WHO Any synth
3. Multiple outputs
WHAT For each OSC / routing lane, there whould be at least one extra additional stereo output.
WHY In a modern DAW world, you can then route outputs to different fx or use it as sidechain etc.etc. or even mangling multiple outputs with different (cross-)processors.
WHO Any of your synth
Thanks for consideration
P.S. You also could consider to do one single fx plugin with ALL of your synths' fxs, and then make it preset compatible with all of them
