I think there are some locations within AST that would benefit from a loading indicator.
There have been some instances where I clicked a control in AST and nothing happened for a few seconds, and I could not tell if I had misclicked the control, if some action was occurring in the background that prevented the action I tried to initiate, or if the action was occurring but was in the process of being loaded.
I think if loading indicators were added in some locations, the application may feel more responsive or less "buggy" even if the actual response times do not change.
Some examples of where this might be useful:
Node Selector: After selecting a large node on the page, there can be a delay of a few seconds where nothing changes on either the targeted page or the Select Node dialog.
DOM Selector: Loading a page with a large DOM can take a few seconds between clicking the DOM Selector button and opening the Confirm Node Selection dialog.
Confirmed Violations/Needs Review tabs: In modules with many violations, the Confirmed Violations and Needs Review instances can take a few seconds to load. Until this point the violation number appears as "0" and nothing appears in the panel area of the tab, which could mislead someone into thinking that there were no violations found for this instance.
Deleting instances: When deleting a large number of violation instances, there can be several seconds with no change after the Delete button in the "Delete Selected Instances?" dialog is activated, and it can give new users the impression that the app has frozen when it is really working in the background.
Adding instances: When adding an instance to a module with many violations, there can be a long delay. This is especially problematic if you add an instance from the Manual Testing dialog and then close the dialog before the instance has fully loaded into the violation list. During this "new instance loading" time, some of the controls are interactive: you can check checkboxes and operate the Delete button on individual instances. However, the Edit, Pattern, and Manual Test buttons are not available, and when the page eventually updates with the new instance, checked checkboxes will get wiped out. If a loading indicator were present or if interaction were disabled until loading occurred, users would encounter fewer "limbo" situations like this.