I mean to use the existing block manager.
Probably in the theme settings, have a option to enable a footer area with some addition settings for styling (colors) and number of columns and their widths.
Like other apps, (such as blog, gallery, and files) the footer would be editable on the front end using the same block manager that's used for pages; using the same blocks, the footer area would be a separate section where blocks can be placed.
For example, if I login to the front end of my website as the administrator, I will see the tab on the left to open the block manager. Once I open the block manager, an outline of different sections where blocks can be placed is shown. The footer should be another separate section for blocks.
Also, once enabled, join the upper footer area with the copyright footer area, so that they appear as a single footer (like normal website footer that have a copyright section and a widgets section.