I don't know either! But thanks for the info!
Right. You don't know. I don't know. Nobody really knows since we have a vacuum of authority to decide such questions that would normally be sent to the Holy Office. I doubt that Tucho's going to have a Catholic answer, and of course he assumes that the NOM is no sacrilege.
Given this "I don't know" situations, any reasonable need for the Sacraments justifies assisting at such Masses. If they did have Mass on a NO altar that's desecrated, they in fact do so not really THINKING it's desecrated, so there's no intention to desecrate, and since it's really a matter of my opinion. Given how I read Canon Law, an Ordinary could for legitimate reason dispense from some of these canonical requirements, so given the state of emergency and the confusion ... I'd say it's licit to assist even if you're not sure, along the lines of St. Alphonsus' probabilism (or semi-probabilism) approach the moral theology, where you don't have to be completely paralyzed due to uncertainty.