As someone working the religion game right now, I think that would be awesome. Personally, I don't think it would need to be complicated, and Unique Item would be good IMO. When the unique item gets donated, you could add a portion to that items wiki page about your religion.
I think this would be a very cool addition to the religion game.
Question: Would the item still degrade? I personally hope no. Afterall, it is sitting in a display, not getting used. Plus, I hate the time crunch of trying to find an Advie, them finding someone to repair it. Huge pain in the butt lol.