Given the difficulty in finding teams to run older content, I honestly don't see a problem with this and feel it would revive some excitement for Xur every weekend. I still remember how crazy everyone got when D1 Xur sold Gallagher horn back in the day. My thoughts: Xur should have a low chance to sell these items and maybe even legendary gear from these activities, with holidays offering slightly higher chances of dropping these items from dungeons/raids that are at least 1 year old.