I wonder what is Slack's TOS? Maybe with their approval, a COPR could be maintained without any issue?
COPR can't be used for building non-free software: https://docs.pagure.org/copr.copr/user_documentation.html#what-i-can-build-i...
Indeed, forgot about that when writing my e-mail ^^'!
I guess someone volunteering to properly package it in RPM Fusion could do it (if they got Slack's approval), since Slack seems to be no longer willing to ship it themselves.