I used to use an ISCO IIIL for years with my scope screen, but zooming is more cost effective and I feel having additional optics in the light path is probably doing the image a little more harm than just zooming. I could probably measure the letterbox bar area to see if there is some sort of non-uniformity, but by eye, it looks just as good as the center of image for both white balance and brightness.
I think a few hours a day having the pixels displaying black, which is the native state of the panel anyways (no voltage being applied to the pixels) shouldn't cause any issues. If that were the case then I think leaving the projector off for extended periods of time would do damage, but that isn't the case. Now...if we were making the pixels brighter, applying voltage, for extended periods of time then I think we'd be seeing issues.
Have never liked the 2,35:1 zoom approach my self.Do not like the static use of the light engine and using only ~75% og the resolution from the 16:9 panels, area/resolving power of the projector lens, and light from the light source when the rest 25% needs to be absorbed in the projector light engine. The extra lens between the projector and screen will add some degradation but not sure a High end A-lens like the ISCO IIIL will reduce the same amount as the 25% reduction of the 75% use with the zoom. This may also depend of the projector the A-lens is used on, think the Z1/RS4500 may not benefit as much as a RS400, but it may also be the need for vertical scaling and stretching to fill the panels, so the picture on the screen will tell the truth.I use a ISCO 4XL on a cine slide, on a JVC RS520, and can quite easily try the zoom and the A-Lens, and think the A-Lens often wins, especially when 4K HDR BD is the source and the extra pop of light is needed. Not shure what reflection state the lcos pixels have without voltage being applied to the pixels, but i think it is the different heat abortion that may be the biggest factor if there were burn in problems this way.I know that Sony SXRD Lcos have had some problem with contrast drop over time in models like the VW1000, but that have been evenly distributed over the entire projected picture, and not acting like a burn in. There were some theories that this happens faster on projectors not used for a long time, than regular used ones. so not burn in related to static picture information.