Frankly, in this series, I see higher probability of May's return than Dawn.I do not mind, but there is very little chance of May's return due to her Seiyuu's voice disorder (and from what I heard, Japan is very reluctant to change voice actor)
We haven't seen May in a very long time. Dawn We saw Dawn later compared to May.
And May is better suited to be a top coordinator. Better squad. More experienced. May T can return as Top Coordinator.
No mention of pokemon contests in the new series. We haven't seen the ribbons for a very long time.
The easiest way to see Ash's Top Coordinator friend and Blaziken in the new series is May.
Dawn may also return due to the DP remake. If Ash catches Piplup, Dawn might return too.
Dawn's piplup becomes the teacher for Ash's piplup.
Dawn or May I think definitely someone will return.