If the addon gpr used the syntax:
gramps_target_version = major_version,
the publish process (make.py listing) will still resolve that to a single version (based on the GRAMPSPATH source tree) and write it to the JSON.
So either way, the JSON will list a specific target version.
That’s how it works now. But the gramps_target_version could evolve to support a list/range. It wouldn’t be backward compatible (unless there was a decision to do a maintenance release for 5.2 and 6.0)
It would be an opportunity to add some fault tolerance for the JSON reader too.
For instance, I found it useful to search on Author or Maintainer (name or eMail address) to find sets of addons by particular developers.
And (eventually), it would be nice to have a link to the preview thumbnail in the JSON. So if the current plugin registering method could ignore columns where it does not recognize the column header, more of the .gpr.py could be included in the JSON. Then we might be able to generate the Addons List for the wiki … and do other not-yet-imagined things too.