[This content is out of date and no longer canon (Various ships/character goals have changed)]

Right. So I have fankids who are currently league members during the Plot and ones who will become league members in the future. I’ll list them all out and note which category they fall into as well as their specialty.
(That being said there are plenty of characters who aren’t developed enough yet to say for sure, so this list isn’t final by any means.)

Kanto
– Sage (Green/Red) will over the Viridian Gym from his aunt (Flying Type specialist) 
– Amaryllis (Red/Yellow) is the current Saffron Gym Leader (Fairy Type specialist) 
– Adriana (Rudy/Cissy – Misty’s stepdaughter) is the current Vermilion Gym Leader (Water Type specialist) 
– Peony (Lt. Surge/Violet) is the current Cerulean Gym Leader (Electric Type specialist) 
– Gemma (Forrest/Janina) will take over the Pewter Gym from her father (probably Rock Type specialist)
– Nerissa (Erika/Valerie) will take over the Celadon Gym from her mother (probably Grass Type specialist) 
– Kestrel (Janine/Falkner) is the current Fuchsia Gym Leader (Poison Type specialist) 

Johto
– Renato (Silver/Lyra) probably will become an E4 member 
– Yuusuke (Morty/Jasmine – Falkner’s stepson) is the current Ecruteak Gym Leader (Ghost Type specialist)
– Luna (Bugsy/Aaron) will take over the Azalea Gym from her father (Bug Type specialist) 
– Lee (Jasmine/Cress) will take over the Olivine Gym from his mother (probably Steel Type specialist) 
– Adelinda (Clair) is currently an E4 member and will eventually become the Kanto/Johto Champion (Water Type Specialist)
– Addie (Karen/Will) (and possibly her brother Eddie) probably will take over the Cherrygrove Gym her mother started (Psychic Type specialist) 
– Draco (Lance/Ethan) is the current Blackthorn Gym Leader (Dragon Type specialist) 
– Euphie (N/Hilda) will likely become an E4 member after he moves to Johto to be with Renato

Hoenn
– Levi (Lisia/May) will take over the Sootopolis Gym from his mother 
– Layla (Brendan/Wally/Anabel) will probably become an E4 member
– Rudy (Brawly/Roxanne) is the current Rustburo Gym Leader (Rock Type Specialist)
– Safir (Brawly/Roxanne) is the current Dewford Gym Leader (Fighting Type Specialist)
– Caleb (Flannery) is the current Lavaridge Gym Leader (Fire Type Specialist)
– Opal (Winona/Kris) will probably take over the Fortree Gym from her mother
– Laelia & Trias (Tate/Mira twins) are the current Mossdeep Gym Leaders (Psychic Type Specialists)
– Apollon (Steven/Wallace) probably becomes an E4 member (gotta one up Levi)
– David (Sidney/Phoebe) becomes an E4 member (Ghost Type specialist)
– Kiran (Archie/Maxie) is currently an E4 member and possible future Champion
– Theo (Tucker/Lucy) is currently the Mauville Gym Leader (Fairy Type specialist)

Sinnoh
– Daniela (Roark/Mars) will take over the Oreburgh Gym from her father (Ground Type specialist)
– Isolde (Candice/Reggie) will probably take over the Snowpoint Gym from her mother
– Ronan (Flint/Volkner) will probably take over the Sunyshore Gym from his father 
– Emery (Paul/Morana – Ash’s stepdaughter) will become Champion
– Natalia (Lucian/Dahlia) is the current Veilstone Gym Leader (Steel Type specialist)
– Maisy (Buck/Marley) is the current Canalave Gym Leader (Dark Type specialist)
– Ceres (Archer/Saturn) is the current Hearthome Gym Leader (Poison Type specialist)

Unova
– Maddie (Rosa/Curtis) will become Champion
– Bertram and/or Maela (Hilbert/OC) might or might not become Gym Leaders of possibly a new Gym in White Forest
– Blake (Cheren/Bianca) will maybe join the E4
– Jerrie (Skyla/Elesa) is currently Mistralton Gym Leader (Steel Type specialist)
–  Cypress (Benga/Iris) might or might not become Opelucid Gym Leader (Dragon Type specialist)
– Micah, Noah & Terah (OC/OC) are the current Opelucid Gym Leaders (Dragon Type specialists)
– Nika (Caitlin/Marlon) might or might not join the E4
– Hymnia (Grimsley/Shauntal) will become an E4 member (Dark Type specialist)
– Gabriele (Giovanni/Archer) is the current Castelia Gym Leader (Ground Type specialist)
– Sunna (Roxie/OC) will probably take over the Virbank Gym 
– Anise, Rosemary & Verbena (Chili/Korrina, Cress/Jasmine, Cilan/Clemont) will reopen the Striation Gym (Fire, Water, and Grass Type specialists)

Kalos
– Basile (Lysandre/Bryony, adopted Cilan/Clemont) is currently an E4 member (Fire Type specialist)
– Cori (Cilan/Clemont) will probably take over the Lumiose Gym
– Lina (Siebold/Alexa) will probably take over the Shalour Gym
– Madeleine (Sawyer/Miette) will probably take over the Laverre Gym
– Margot (Alain/Mairin) will become the Coumarine Gym Leader (Dragon Type specialist)
– Azariah (Tobias/Rafe) is the current Anistar Gym Leader (Dark Type specialist)