A formula cell also is an option to choose when user open a filter window. In the future we should consider an API that will allow developers to choose if any row should get excluded from the list an remain always visible but this is a plan for further future.
If the amount of rows change you can alter the SUM calculation via afterCreateRow and afterRemoveRow hooks. They return an index and amount for rows that has been added or deleted. The same operation should be possible if you allow to move rows.