Not much chance of Carol Marcus or David Marcus showing up, as Merritt Butrick had died even before SIVI had been made. Bibi Besch was still alive and working, but she would die of complications from breast cancer in 1996.
And I think showing a younger Carol probably would've just made it look like Kirk was robbing the cradle.
I'm picturing the same idea of Kirk making breakfast, with like a five year old David and Carol in her late twenties. So they'd obviously cast a young child as David since they sadly couldn't do anything with an adult David.
Kirk having a bro camping trip with Spock and McCoy would've been sweet. Having him be forever the young captain of the original Enterprise would've made a lot of sense too.
And yes, Edith if they could have done it some way, some how, would've been amazing. I'd have cared when Kirk lost Edith again, it would've been devestating. Losing David again would've been devestating. I didn't give a damn about Antonia, so I didn't care about what Kirk was losing, and I don't think anyone did. I don't even think Kirk really cared that much.