Additional board subscribers permissions toggle - Only see items for which you are assigned as owner

Hi. It would be really grate to help manage confidentiality if there was an additional toggle for board permissions. That would be the ability to set the board such that subscribers can only see rows they have been assigned to. This would be a quick way to manage confidentiality without having to use multiple boards.

Use Case - There is a board run by (in my case en engineer/design reviewer). This person is commenting on designs submitted by various people from different external companies. The reviewer does not want subscribers from one business seeing comments made on design submitted by another business. The reviewer does not want subscribers to be able to see comments until they are ready to be published. I appreciate that all this can be done using separate boards. But why make multiple boards when one will do?