Thanks for that. I would expect some way to configure that. Removing that line would also apply that to all widgets areas, on all themes, right?
My workaround is to add a plznohide class to the appropriate widget areas' divs and add this to either my theme CSS or the "Custom CSS":
.hidden.plznohide {
display: initial !important;
visibility: visible !important;
}
It seems to work as expected. Being able to configure if each widget area should be hidden in the ACP would still be nice.