I don’t know if I can add a feature
In the list view, if a column is a number or currency, the function of automatically calculating the sum is added at the end of the column. I don’t know if I can simply modify the code implementation.
You would need to modify the view.list.php to add you Custom JS which can sum up the column that you want and then add a DOM element at the end to show the sum. Needs custom coding but its pretty much possible.