This should be a trinary toggle available on the main window like claim visibility toggles.
Options are:
Off
Area Selectable
Memorized
Off would have the Ui function exactly as it does now. Area Selectable means you can click-drag-select in the fashion of the old land management UI. The window should be added just a bit to with an indicator for the actual # of tiles and dimensions in XxY format. Right clicking would cancel the current selection and left-release would execute the desired action.
Every selection made is stored into memory but only the most recent selection is retained. Memorized pulls up the last XxY dimension you selected with Area Selection and follows the cursor. Left Clicking executes the desired action.
The "desired action" is any landscaping task or planting. By having a seed in the cursor-hand the area select behavior becomes active if it is toggled on or memorized mode. The others initiate the area select behavior by having their ui modes initialized under AS or Memorized modes. A -> n -> (H/G/P/L)
The task is repeated for every tile along some path-finding algorithm/loop until resources are exhausted or the selected area is complete.
This would require minimal UI programming as it could make use of currently existing functions. In addition, it lays the foundation for more advanced automation in the area of farming for a braver day.