Upvoting as well!
In my opinion, this is an absolutely essential feature. Philosophically, transclusions exist for the cases when the data belongs equally well to more than one place. Yes, there are other cases perhaps where you simply want to showcase data, but in many many others, the goal is for the data to actually LIVE in more than one place. In order for it to really work, it should be virtually transparent that it is an embed rather than just a part of the note, and for that to happen, of course, it has to be editable.
Yes, you can get something approaching the same effect with the Hover Editor plug-in (which is awesome), but there are two issues with that solution.
First of all, it says right in the readme that Hover Editor is forced to use features outside of those officially supported by the API, which means that it’s going to be really hard to maintain, and probably won’t last forever for that reason. That’s because when a plugin has to rely on features outside of those in the API, they can be, and often are, broken or removed later by the Obsidian devs (because they aren’t officially supported), which breaks the plugin.
But second of all, and more importantly, while that plugin is great it hardly mimics the effect of real transclusions (editable embeds) that exist in many other note apps. The practical difference may not be massive, but the impact on UI and user focus is very significant. When I use an embed I intend for the information to LIVE in both places. I don’t want to see a difference. When I do, it pulls me out of the moment and, worse, makes me miss Roam ;).
Anyway, I hope that all makes sense. If others prefer embeds to not be editable I think it would be perfectly reasonable to make it an option, either globally or per-embed, for it to be view only, but for me I would LOVE for them all to be editable.