At this point its hard to tell because judging by past patterns Cilan destiny in this show can go either way. Usual response will be how he is bound to leave because of advertizing purposes,m to make room for new character etc, etc with people basing responses on main females and writers practice of replacing them after every few years.
However going by Jessie, James and Meowth as well Brock example which aren't pokemon main stars like Ash is serves as indication how writers can depending on popularity, circumstances and their own motivation keep characters in main cast from previous generations for extended period of time successfully promoting new games through older cast as well.
So its not completely out of option to expect Cilan staying around, if anything other than being pretty inconvenient and useless to start tradition with male supporting cast changes after every few years as well. Its already bad enough we have girl characters replaced like they're on assembly line with decline in ratings reflecting people annoyance.
It would be certainly welcomes twist in current formula to give us someone stable who could stick around for longer to make sure everything is running smooth, and get more development.
To maintain popularity of long running show you sometimes need stable cast in who people can invest starting to grow on characters, which reassures viewers staying loyal toward some anime increasing its appeal to wider group of people.
No. He has no relevance to Gen 6 and Brock staying for multiple gens was considered a mistake. They won't repeat that.
Who considered it to be mistake? I doubt writers did, otherwise we wouldn't have Ash and TR stick around for so long.
I don't understand why people keep bringing up past characters as reference points. Do you really think if Kanto/Johto were written the way the show is now, that either Misty or Brock would have continued as long as they did?
You do realize Brock and Misty were originally intended to stay permanently in main cast?
I seriously doubt it. Iris proves they don't need to take the main female playable character either, they can just take another random girl Gym leader.
Something which can go both ways meaning possible reuse of already existing or older character too depending on circumstances. After all its easier to carry over gym leaders to different regions than its case with game protagonists which are more tied to specific generation they originated from.
