Max is actually the more likely Hoenn companion to return, as May's Japanese VA is retired from what I've heard. Max himself also has a VA situation, but unlike his sister he would need a new English VA if he ever returned.
With Bea appearing again I now consider her Ash's primary rival of this saga, which would mark the first time that Ash's primary rival has been a girl. Volkner is the only character who I can definitely say is returning.
Back then Ash didn't have a companion whose goal is to catch em' all, and Ash himself has received less focus this saga than ever before. I'm not confident in Ash catching anything more, especially considering that they are bringing back reserves and whatever Ash could catch could just as easily...
Pokemon games usually have new announcements in May. ORAS and LGPE were revealed there and we got the first real information about SM and Sword and Shield there. I think that BDSP and LA would have been revealed in May if this year wasn't the 25th anniversary of the series.