Well I just wrote a nice long note explaining the issue we’re having with this new endpoint, and it has been deleted as spam. 
So I’ll write a shorter version and see if sticks. 
We have a service that receives a webhook when a user fills out a form on our HubSpot CMS site. The form includes a file upload. The files URLs now have the new format.
Unfortunately, our service can’t retrieve files anymore since this change. Adding our HAPI to the querey string doesn’t help. Using OAUTH headers on the request doesn’t help. No matter what, our service is sent to a login page meant for a human and dies with a 503.
We can call https://developers.hubspot.com/docs/methods/files/get_files_file_id with the filename and see information about the file. But there’s no longer enough information in that API response to get a working download link either.