That's a good idea.
Will do when I get my sources in order (them all have GPL comment header when it should be LGPL).

P.S. I just tested my idea with using hardware scaling (FullHD is too much for RPi 2, it glitches with incomplete buffers ) and it works well indeed.
I had to add some hacks to my engine to utilize this, such as virtual window client rect (different dimensions from the real client rect)
When you stretch the window top the whole screen, the render surface stays limited to 1280 width or 960 height, whichever allows for square pixel aspect, and the surface is stretched by hardware to match the window.

RPi is totally capable of 60 FPS but you have to jump through some hoops to get there.