When adding fields in the shared space which is intended to be used be several workspaces it is default added for all and cannot be hidden either.
It might be relevant to only 50 out of 100 workspace, but still its viewable for all.
I think you should create business rule (for all entities) which enables workspaces to hide certain Shared space fields in the IU when they are not needed
Shared space doesn't mean it is relevant for all workspaces.........this is exactly what you're also doing with Shared Relase, Application modules, Manual Tests, Epics etc. Please change mindset on this:)
...a condition should automatically be added on the space level rule so that this particular workspace it out of scope.
If this is too advanced.......workspace admin should get a warning saying this field is required on space level and an expection needs to be added for this workspace before field can be hidden