Ok, this seems to actually work for Gnome 3.34:
1. Comment out ExtensionUtils and add ExtentionManager in the declarations:
//const ExtensionUtils = imports.misc.extensionUtils;
const ExtensionManager = Main.extensionManager;
2. around line 1214, change:
ExtensionSystem.connect('extension-state-changed',
to
ExtensionManager.connect('extension-state-changed',
3. around line 1250, change:
let ext = ExtensionUtils.extensions[uuid];
to
let ext = ExtensionManager.lookup(uuid);
Next thing to tackle is all the "object.actor is deprecated" status messages filling the queue...