Hello Andrew,
Thank you for your question. You are correct, profile images are now exposed from pbs.twimg.com, which should be seamless and reflected in the profile_image_url and profile_image_url_https exposed by the REST API. We have updated the documentation: [node:10796].
If you encountering any 403 or 404 errors while trying to access profile images, please make sure to update your user objects by calling the [node:10320] endpoint.
Please let us know if you have any other questions or issues.