True enough, but in let's say five years, projects will be up to 4K resolution, or maybe even 8K resolution. If you scanned for 8K resolution, right now the projector won't do your scans justice. But in five years?
nope. 4K won’t even be noticeable. In order to benefit from 4K, you would have to double your display size if everything else remained equal. The funny thing about display resolution, is once you reach the point that you can no longer see individual pixels from a given viewing distance, adding more pixels does not improve the visible image sharpness. You can grow the size of the displayed image and maintain the same sharpness, but jamming more pixels into the same area does nothing once you can’t see the individual pixels any more.
In a projected display environment, unless the audience is sitting close enough that you can see individual pixels at whatever the projected display size is, replacing the projector with a higher resolution projector does nothing unless you either move the audience closer to the projected image (making the image appear larger), or you move the projector back to project a larger image, and even then, you’d basically have to double the projected display size to benefit going from Full HD to 4K. At some point, you can’t make it bigger. The same goes for the HDTV in your house. Buying a crispy new 4K TV does nothing unless you buy one that is twice as big as the one it is replacing, so if you had a 50 inch HDTV, in order to get any benefit from that extra resolution, you’d basically have to replace it with a 100 inch 4K TV, assuming you could actually get any 4K content that really was 4K (meaning captured at higher than 4K resolution and downsampled to 4K), OR, replace it with the same size TV and sit a lot closer to your TV. At some point you can’t sit any closer, and/or can’t make it any bigger without making the wall/room larger.
For display environments, the sweet spot is Full HD/2K, and will be for quite some time to come. You may not realize this, but the vast majority of movie houses have converted over all of their systems to digital projectors over the last 5-10 years. Guess what resolution a lot of those projectors are? The smaller screens are 720p, the medium to large screens are 2K, or FullHD, and the really big screens are maybe 4K, but usually 2K/FullHD. Those projected images are indistinguishable from the Blu-ray movie you watch on your big screen HDTV at home even though they’re both similar resolution (assuming the projector was properly set up and in focus). The vast majority of Hollywood movies are mastered at 2K resolution. Yes, they shoot at 4K and up, but that’s so they can oversample and/or reframe the image in post and still have a 2K image that is as sharp as it will get.
fullHD/2K is the point of diminishing returns because the individual pixels are no longer visible in the vast majority of viewing environments. This is why 720p/1080 was selected as the HDTV broadcast standard. It was a 9x jump in resolution over SDTV and was sufficiently high enough resolution in 99.9% of the places it would be seen that they wouldn’t need to make any changes for quite a while. 4K, 8K and all that other stuff is just stuff so that the manufacturers can keep selling you more stuff. It will only lead to a sharper image in certain very specific viewing environments, and our TV rooms are not those environments.
if the OP really wanted future proof, scan it in at 4K or 8K, then down sample it to FullHD. You’ll have an amazingly sharp and detailed FullHD image that upscales wonderfully to any future display standards without losing much if any sharpness, and it’ll still be a small and tidy file.