rpc class could use Evented mixin and have:
4 local events: start, end, success, error
2 global topics: rpc-start, rpc-end

Global topics would replace current IPA.hide_activity_icon(); and
IPA.display_activity_icon();

'start' and 'end' local listeners would call custom functions in situations when global activity widget is not shown.

'success' and 'error' would call on_success or on_error methods.