Pokémon Showcases

Misty, May, Dawn, and Iris absolutely

I don't like Lillie but she has an interesting story

Bonnie is only if she's grown up (and Clemont better have some role in it!)

Mallow maybe

Same goes for Lana

Chloe was a wasted character that had so much potential

I've already said how I feel about Serena so no need to again

That's S/R

We're talking about the ones in Kalos

Oh, sounded like you were talking about the generality.

Afaik, there aren't any Coordinator contests in the Kalos region. Kanto, Johto, Hoenn, Sinnoh are confirmed since May competes in Hoenn + Kanto before heading to Johto at end of series. Dawn competes in Sinnoh(with May returning for the Wallace Cup that rotates between the regions but counts towards each regions Master class tournament) before heading to Hoenn(if memory serves) to continue competing for Ribbons. Dawn's return in Unova was basically to get a break and to surprise Ash. Not sure if Unova has Pokemon Contests.

For Kalos, they just have Performances and are female only. That is why Serena goes to Hoenn to brush up on Coordinating because it'd help develop her Performance skills(and Battling skills too). Meaning if they did a side series, Serena and Dawn would be a potential duo but thanks to Journeys, it's Lisia, Serena and May as a performing trio. We won't get anything though because of KAORI.

We did miss our on a lot of off screen development though. Yet with the passage of time, characters such as Max and Bonnie could see the light of day.