Microsoft has begun the "gradual rollout" of dynamic arrays on the monthly channel of Office 365. This is great news, although Microsoft will not be drawn regarding how long this rollout will take to complete as they are "...[monitoring] the feature health and user feedback...".
Hopefully, it will be too long. It's also noted that dynamic arrays are still offline on Excel Online - there has been no further update as to when these coll features will be back. Keep watching this space and we will keep you informed!