Custom Report - Inherit the 'Show Column If' to enable / disable Dimension/Measures
it would be very interesting for us to have an option to show/hide certain fields from the master visualization. So if the result of the 'Show Column If' expression from the fields in the master visualization can be used to show/hide these fields in the Custom Report Dimensions/Measures that would be fantastic!
There is actually a release coming later today that will let you do this (and quite a bit more) by using groups for dimensions and measures. Take a look at this video for an introduction and step by step how-to for groups.
You can decide if anything uncategorized should be included and by using expressions you can choose which groups are shown in different situations.
Apart from that new feature I would also suggest taking a closer look at defaults, presets and bookmarks in the Custom Report so that you can help users get to the right setup more quickly.
I hope this helps.