- Possibility to deactivate the "simultaneus 3D rendered view" to speed up performances on older systems. Yes the 3D view can be hidden but I'm not sure if it does deactivate the portion of code for 3D render in the background.

That is a feature I would very much like to see. The 3D window rendering is VERY inefficient because it keeps stacking and executing rendering commands with every move/action even if a previous render has become useless. I'm not sure if this is a Sweethome3D problem or just how Java handles the stack of rendering commands but it could be much more efficient if invalid/unneeded rendering actions were terminated. Currently it's so bad that if you close Sweethome3D the last rendering still keeps executing until it's finished while the window is already closed. Stopping of obsolete rendering threads is badly needed but I'm not familiar enough with Java if this can be done.

A button to temporarily stop the 3D view rendering would be a first step to at least solve the problem when working with large projects where every click initiates a new full redraw where you only want to see the result after a few more actions.