At the moment dynamic arrays are not even in the production version of Office 365; they definitely missed the cut for 2019. I am not sure what will happen once DA have been available within 365 for a while. For me, it is not simply a matter of having a cute function or two available. It changes the way in which I solve problems. All my solutions now start with the assumption that the solution will be completely array-based, with the '@' implicit intersection operator very much the 'solution of last resort'.
If MS does not retrospectively implement in Office 2019 then I will be doomed to remembering the old techniques for years to come :-( .