A useful feature which has already been mentioned is the offline editing functionality (Link).
Maybe this requires a little more specification, as the response included the need for a virtual windows environment. IMO, the need for actually running the plugins is not required (as this would remove the need for the engine completely, and as I understand the Windows env is only required for the VST virtualisation), but an option for editing the plugin states based on what is saved in the exported file would suffice. A library of hard-coded plugins (basically all VST3s that have been tested for compatibility) with their known plugin parameters would allow users to prepare and edit showfiles which is what OP originally intended and would remove the need to actually have the plugins running or licensed. The user would just have to be aware that loading plugins that they are not licensed for wouldn’t work in production.
TLDR: we just need to be able to edit the file without the engine.
What am I missing?