I like this idea, but I do have a concern. This would restrict being able to split a pinned pane. But there are some possible solutions.
Assuming the pinned pane isn’t the only open pane, maybe the split off duplicate of the pinned pane could be opened immediately to the right. This would be assuming that right edge is not a pane region interface border. In that case, it could be created immediately adjacent to the pinned pane splitting an adjacent pane that has the space.
Anyways, perhaps this could be a toggle in the settings.
Thanks.