Currently, this is part of the process-svg addon. In order to annotate the SVG, data from Data Index is required anyway. We should remove the 
/svg/processes/{processId}/instances/{processInstanceId}  endpoint so Data Index GraphQL processisntance.diagram retrieves the source file from the runtime, and then executes the logic to get node instances information locally and then annotates the SVG.
This will remove the round trip needed back and forth between runtime and data index in order to display the SVG information in the management console.