It would obviously be better to have scaling of the RGB formats directly and not have to waste time with the color conversion, and I don't see how it could hurt to have a request for the feature. I'm fairly new to all this maemo stuff, and software development in general, so it would probably be better if someone with a bit more knowledge about these things than me would write the request.
Actually as I've written in the quake2 thread, I've optimized the conversion to a point, where even with overhead caused by it, the SDL_DisplayYUVOverlay with a 400x240 image scaled to 800x480 seems to be so much faster than doing SDL_UpdateRect with XSP pixel doubling that it actually gets better fps with the overlay. Also, with overlay, I can do partial screen updates, which I believe is broken with XSP. Though I've not yet made an version of UQM to use the faster version, since it will need some changes to make it work with 16-bit surfaces, where quetoo uses only 8-bit, and I've been a bit busy with other things lately.