To consider:

1) Right-click in empty (or non-empty?) non-gap cell offers DeleteCell action (=delete row and column)

2) Right-click in empty (or non-empty?) non-gap cell offers AddRowAndColumnAfter, AddRowAndColumnBefore and/or SurroundCell action (=add one column and one row to bottom right from cell, or to top left from cell, or two rows and columns surrounding the cell from all sides)

3) Click on row/column header selects components in that row/column

4) With gap support on: holding Ctrl when moving or resizing components by mouse overrides the gap protecting mechanism, allowing component positioning in gap cells. When dragging, the target cells are not emphasized in green but in red in such case.

5) Modify design of headers to make them more welcoming for user action

6) Click in gap row cell (resp. gap column cell) selects the row (resp. column). Selected gap row/column height/width can then be adjusted individually. Allow gap row/column/cell(=both) by mouse; e.g. by providing resizing handles when gap row/column/cell is selected, or by providing resizeable gap row/column headers

7) Add Toggle Button beside the "Show/Hide Empty Rows/Columns" to enable "Trim bottom/right empty space". If switched on, this would cause the grid to be always kept in minimum size (no empty or gap cells to the right and below the bottom-right-most component)

8) Make the constant used for "acceleration" settable in property file. (acceleration = increase/decrease of Insets, Padding, Position, Size, etc. by more than 1 when clicking the respective buttons with Ctrl pressed. The current hardwired constant is 5.)

9) Add a handle to bottom right corner of grid layout when gap support is on, enabling "resizing" the whole layout, i.e., increasing/decreasing the size of all gaps uniformly at once