Unfortunately, streaming quality isn’t as high as Blu-Ray quality would be. And also unfortunately, if it’s not released on physical disc or, at minimum, a purchaseable download (versus streaming subscriptions), working on an edit using material from it would mean that edit can’t be discussed at fanedit.org or listed on IFDb due to their extremely strict “own the source” rule.
Sadly, though, I agree - it’s unlikely that The Mandalorian will be released on physical media in the forseeable future.
If something isn’t commercially available on physical media, I feel like being subscribed to the service where it is commercially available should count as “owning the source” for the purposes of fanediting. Either way you’re circumventing copy protection, which isn’t strictly speaking legal due to the DMCA in the US. As media moves from an ownership model to a subscription model this will become more and more of a problem for faneditors.