ziguara: if someone had a 320×240 display, currently it out render to 640×480 and scale to 320×240 – with the proposed change it would render to 320×240.
The downside of these changes is basically just for RPI1 users with HD displays – if they don’t lower the overall render resolution, they may get performance problems – especially using shaders. But it would be easy to switch.
Yes if you ran it on different displays performance could vary. The old behaviour would be switchable from the config editor (I’m putting in some settings for it now)