Sorry for taking so long to close the loop on this thread in Topliners. For the last several quarters we've had a closed beta running to prove out the editor infrastructure changes and enhancements I mention above related to security across all the editors and WYSIWYG editing capabilities in the HTML upload editor. As part of this beta you can also opt to turn of the whitelisting of content in the editors and that will allow for the insertion of any JS or tags, either into the header using the snippet tool or in a Shared Content section that gets placed in a landing page. Note that using a shared content section is great for things like 3rd party analytics or scripts you want placed on every page because it allows you to make changes in one central location that will then propagate to every page that has that content inserted.
If you wish to participate in this beta please open a case with support requesting access and product management will review the request.
thanks,
Stephen