How To Assign Custom Domain Names To Profile URLs
Jamroom Developers
It worked OK when everything was http, but now the push is towards using https which made it much more complicated to keep working.
Then browsers tightened up their javascript policies making it harder to make javascript from one domain work on another.
and then on top of that services like CloudFlare have come along to provide extra caching which adds an extra level of complexity needed to debug why its not working when it stops working.
When something went wrong, the level of support required to figure out what needs fixing is "arrgh".
So it was retired.