Describe the project you are working on

A 3D game that involves a lot of SubViewports to render textures on the fly

Describe the problem or limitation you are having in your project

Debugging issues at runtime with the procedurally generated textures can be incredibly difficult because the output in my scene only displays the layered result of multiple combined subviewports

Describe the feature / enhancement and how it helps to overcome the problem or limitation

When editing a scene, it's possible to see a preview of what's rendered in a SubViewport if you select it in the inspector. This isn't available when inspecting the remote scene tree if you launch the game, which I'm currently sorely missing.

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Same behaviour when selecting a subviewport in a local vs. remote scene. Can't say what this would take under the hood, I'm not familiar with the limitation that caused the omission in the first place (I'm assuming there was a technical reason for this not to be made available)

If this enhancement will not be used often, can it be worked around with a few lines of script?

No

Is there a reason why this should be core and not an add-on in the asset library?

It's a core piece of remote scene/inspector functionality