I think this could be a useful feature, but I figured I should mention that this forum is only for users, so feature requests here will not be tracked or potentially acted on. Not a bad idea to discuss ideas here to clarify the request, but to make it onto the official wishlist someone needs to open an issue on Gitlab either directly at
or in KiCad with About KiCad > Report Bug
Edit: The work around for now would be to open up another instance of the schematic editor at the same time, just looking at the sub sheet. You’d have to be super careful not to change anything unintentionally though and it still runs a risk of file corruption.