My other fear with a lens system is that it is yet one more complexity variable for my family. They are going to struggle with hitting a button on the remote to do a memory preset for zoom, shift, focus, and that is just hitting a button, not manually sliding a lens into place or back out.
This is what I like about the fixed Panamorph lens, when I first read it. All that you have to do is push the zoom buttons on the projector to get the right size. Just like cycling through the zoom, stretch, etc. modes on an HDTV. So there is no need have to worry about having the family move the anamorphic lens in and out of place. But truthfully, by wife never even realizes to cycle through the aspect ratio buttons and just watches it as is. I walk in and immediately notice that it doesn't look right right, find the correct aspect ratio for her and tell her "doesn't that look better". She rolls her eyes at me and sarcastically says "yes". So truthfully, my wife wouldn't mess with any of that stuff, even if things are strangely stretched and/or 1/3 of the image was not on the screen. But, I would prefer having that ease of use. If I go this route I would probably just do some cheap and simple curtains to slide and cover the black bars on the side of the 16:9 image.
So if there is a 2.35:1 movie you push the stretch button and walk over and slide the curtains out of the way.