Yeah, I find it funny how a lot of good sounding ideas get scrapped in the long-run for the series. Barry Burton was replaced as the story changed, and also Sheva was introduced due to all the racist controversy the game had before it released.
Again though, they seem to be pulling from some of their previous ideas as each title comes by.
Sheva was never introduced due to the racism "controversy". She was in the game from the beginning of its actual development. Barry was only in concept and was scrapped pretty quickly. None of the storyboards seen in the artbook were developed any further. They were drawn before the story was actually completed, and before the game began development.
It's true that they take scrapped ideas though, quite a lot. Grenades and armor were originally in 1.5 but were scrapped to maintain the "survival" aspect, but they were worked into BH4. The Ndipaya in BH5 were actually in the first version of BH4 which became Devil May Cry. Spencer was in every version of BH4 except the last one we got (but his original face became Saddler's) before being put into BH5. The "Hallucination BH4" version featured the Progenitor Virus and Spencer's castle, both were eventually put into BH5. There's a pretty long list.
At least that would be some sort of closure.
Capcom loves adding new characters for RE, yet they seem to forget about them as the games go on story wise.
Exactly what are
They really need to just up and tell us what everyone is doing.
Carlos will never appear in a main game again because he was initially written as a "gaiden" character, likewise with Nicholai. Jill already has been explained (she was chosen as a test subject for P30 specifically to see if it could cause damage to a subject's body over a long period of time, and she was left physically and mentally exhausted by the event's of BH5). Claire isn't much of a main character anymore. Billy, Barry and Rebecca aren't really that interesting, Barry should be in his 60s by now, Billy already received a send-off and is better not seen again and Rebecca is... Rebecca.
Rebecca wasn't given an epilogue in BH3 because the scenario for BH0 was not yet complete, at the time it was expected that that game would have explained what happened to her after the mansion incident. However, for some reason or other, they didn't do this, they kept it as a strict prequel. Claire was able to receive an epilogue because the scenario for CODE:Veronica was already finalized. It was a matter of Mr. Kawamura not being allowed to tread on the toes of FLAGSHIP, who were in charge of the series storyline at the time. It's assumed that Rebecca just bailed out. She never joined the other S.T.A.R.S. members and isn't mentioned anywhere after BH2 except for one file that states she survived.