Symbols would be the ideal placeholder for plugins to set up parameters (in pluginData) for later customization in symbol instances, but, once again, the edit context ruins it for normal use. (You have to drill into the symbol instance to make any modifications.)
I realize the the edit context has large architectural issues, but I would ask you (the Adobe XD plugin team/advocates) to bring up to the XD architects the fact that the edit context is currently wildly over-constraining plugins.
E.g., the most common thing for a data publishing plugin would be to mark a given mask group’s contained shape, and later filling in (when the mask group’s shape is no longer directly selected) “from above” on user request.
Same for a symbol instance, where a plugin would like to make the kinds of changes permitted to a user directly-selecting subparts.
Same for a repeat group, where a plugin building say, charts/graphs, would need to actually modify the shapes involved, not just fill in text or graphics.
I would hope the plugin community would upvote this hugely, so the XD architects could see that this is something long-term that should be solved. Perhaps something of a “user revolt” is needed.
(Anyone supporting Edit context rules for mask groups killing us should move his or her vote here.)