My thinking is to move interface to another layer, currently on how I have my render and sim threads sort of indepedent of each other. Instead of rendering and handling interface on the sim thread as seems to be usual, I'm going to move interface handling to independent phase that is controlled by the sim.
It will run concurrent with the sim thread, will handle loading and unloading of interface resources, and will have links to the controlling data. It will be up to the sim thread to destroy watches. Need to put some more thought into how I want rendering to actually take the info to display. They're really just basic objects passed to the render interface. An overlay can actually probably be done at the same time the scene is rendered. But 3D interface will need the depth buffer at least. Either way, using just the depth buffer once it's displayed, all of the interface can be rendered concurrently.