This feature would not be used by as many folks as the Google fonts or Typekit integration, but it would attract enterprise-level clients who would require it to do their job effectively. Hoefler & Co. are the cream of the crop when it comes to type design, and their legendary status is cemented every day by the global brands using their type.
cloud.typography isn't fonts.com—H&Co. is a legendary foundry and cloud.typography was built for enterprise web design. It belongs on the list of integrated solutions alongside Google fonts and Typekit, as a serious solution for designers and brands whose type needs to be on point.
They have security measures which prevent traditional webfont downloads, so they are a unique case which is just begging to be supported for serious, type-obsessed designers.
It is not possible to download webfonts for upload. It is also unclear if it's possible to use custom code injection to use the fonts—but the clients who are attracted to cloud.typography will more commonly be running massive operations where not having type in the designer is a non-starter.