If something is oversubscribed, it means there are more people signed up than they have space for. It's very popular and crowded.
The outlook refers to the Copts' future. If the world just watches passively, instead of taking action or speaking out against those who persecute the Copts, the Copts' outlook, or future, upsets Adel Messeh. Adel Messah is worried about the Copts' future.