Adding progressive video, would not be an electronic issue, just something that is rare because demand in PAL regions is usually deemed unnecassary. Sony*, Metz and Loewe all have TVs with YUV on Scart but at 15KHz (UK). * Can't confirm this but a rep told me.
Adding progressive through Scart is alittle more difficult. The Peritel connector (scart) is crap. It was invented by some short sited fool, to allow a compact and convienient standard. Separate connectors are generally considered a much better option. Because of the limitations of Scart, the increased bandwidth of video @ 31KHz would I believe cause degradation. The most likely issue being banding or halo's.
The Epson projector has a 1280x720 LCD panel in it so is perfect for progressive 720. Compatability with higher resolutions need not mean better images. Feed it with 1080i and the unit will down scale it to 1280x720. If the internal scaler is crap, then the image will be littered with artefacts. I have not seen one so I am simply professionally speculating.
RGB and YUV are both forms of Component video, but the similarity ends there. You cannot plug a YUV source into an RGB input and expect to get anything and vice versa. It must be transcoded first. Has already said graphics are really best displayed in their native video format i.e. RGB and preferably with H&V @ 31KHz