The GUI is scaled, but not the 3D rendering of the geoscape and battlescape, correct?
Yes. Maybe I was not exact enough. Whenever another resolution than 1024x768 is used Menus & GUI are up- or downscaled which results in blurry GUI & menu gfx.
Ofc. 3d vectors on battlescape & geoscape are always rendered at the selected resolution, but still we have some other scaling issues with the textures also, but afaik those are not related to the fixed resolution stuff (IIRC trilinear texturing is turned off by default, high resolution textures are used 'too late' or at very high zooms only).
Why I wrote that 1024x768 in a window will show the sharpest version is not only related to the GUI & menu stuff, but also related to scaling behaviour of modern TFTs, so if you play 1024x768 fullscreen on a 1680x1050 TFT-Monitor, the monitor will scale that resolution to its native resolution & the result will be unsharp again also for the 3d graphics & textures... (I think this is also what Geever meant)
But this behaviour has nothing to do with UFO:AI's rendering & scaling behaviour, but with the fixed pixels & native resolutions of TFTs & you will have no problem with bad scaling if you use a CRT-Monitor, which will show you sharp 3d gfx @ any resolution...
I'm confident that the blurry textures rendering issue will be fixed soon also...