This request involves the option to create one or more custom 'associated' views to be used in the subgrids. Currently you only have one Associated view, but this view is not available for the subgrid, only the public views. When creating one or more specific views for a subgrid, these views will be publicly available. This will increase the number of views to select throughout the system while the specific subgrid views are not likely to be used in other occasions since they are tailored to the smaller subgrid widths.
Say there is a business case where the users require a subgrid view of Opportunities on the Account form, and they would like to be able to select on 'Open Opportunities' (Default), 'Lost Opportunities' and 'Won Opportunities', this would imply that we create 3 new public views based on less columns and smaller widths alongside the already existing public views for viewing all Opportunities in the main screen and a variety of other views already defined for the Opportunities.
I have played around with disabling views after configuring the subgrid based on these views. This will give me de desired result during the session, but the next day the disabled views are no longer available in the subgrid.
The option to have these views not being 'publicly' available would help in improving the user experience, especially for entities that already have a lot of views.