We have built some integrations with Mux previously, but it isn’t something we have any plans to make available on lower plans at this time: GitHub - discourse/discourse-video · GitHub
We’ll keep this topic on our radar though.
Also worth noting, you don’t need to upgrade from Pro to Business just for storage. You can purchase “extra storage” on the Pro plan if you exceed your site’s allowed storage. Per our pricing page:
Please contact our team if you want to discuss that option.