Switch completely to Gio for icons and it fixed the startup/lookup time for icons. Now works with every icon theme. Taglist/Tasklist/Window switcher still rely on WM_CLASS and WM_NAME to match the icon name, this probably can't be fixed in a sane way

awesome/src/widgets/taglist.lua

@@ -82,7 +82,7 @@ local list_update = function(widget, buttons, _, _, objects)
           id = "icon_container",
           {
             id = "icon",
-            image = client.icon,
+            image = Get_icon(client.class, client.name) or client.icon,
             resize = true,
             valign = "center",
             halign = "center",
@@ -95,8 +95,6 @@ local list_update = function(widget, buttons, _, _, objects)
         widget = wibox.container.margin
       }
 
-      icon.icon_container.icon:set_image(xdg_icon_lookup:find_icon(client.class, 64) or client.icon)
-
       tag_widget.container:setup({
         icon,
         strategy = "exact",

awesome/src/widgets/tasklist.lua

@@ -22,7 +22,7 @@ local list_update = function(widget, buttons, label, _, objects)
 								valign = "center",
 								halign = "center",
 								resize = true,
-								image = object.icon,
+								image = Get_icon(object.class, object.name) or object.icon,
 								widget = wibox.widget.imagebox
 							},
 							nil,
@@ -114,8 +114,7 @@ local list_update = function(widget, buttons, label, _, objects)
 			task_widget:set_bg(Theme_config.tasklist.bg)
 			task_widget.container.layout_it.title:set_text('')
 		end
-		task_widget:get_children_by_id("icon")[1]:set_image(xdg_icon_lookup:find_icon(object.class, 64) or
-			object.icon)
+
 		widget:add(task_widget)
 		widget:set_spacing(dpi(6))