Called Flugladen again. Super helpful and friendly agent this time. He said his colleague already took my ticket off the refund queue yesterday, they have full control over the ticket again and will try to rebook me for September.
He just wasn't sure if it's possible because he, too, mentioned that there's a +- 3 day window for schedule changes. He said that the Corona virus would probably allow for more flexible rebookings - but the AY website says they will only rebook China flights until the end of June. I guess we'll see. If they refuse to rebook me, I'll look into those EU261 rules.
By the way, AY has cancelled China flights through the end of April now.
Really interesting: They were still selling CAN tickets for April on the AY website yesterday and ITA Matrix also showed availability. But on ExpertFlyer, the inventory was already pulled.