Realistically, he'll probably spend another year in Juvenil A since he hasn't become a starter there yet, then 2 years in the B team, then either take the route of slowly training with the first team and being reserve or going out on loan for playing time. All of that is 4 years which would be foundation for him to break in as a true rotational player in the first team capable of fighting for a starting place.
There's room for him IF Samper doesn't become more mobile, we don't buy Oliver from Atletico, and the CM we do buy for the next few years is transitional and not long term (someone like Pjanic who is great for depth and to backup Xavi or even act as a starter for a while or Rafinha playing a slightly deeper role for a few years).
It's difficult for Kaptoum but he has so much quality and fits like a glove (much better movement than Samper, natural Barca CM unlike Rafinha, free unlike Oliver and with better physicality). Too many options in the future for Kaptoum to have an easy and direct chance, but if he has the opportunity his success would be one of the best of the options I believe simply due to his perfect style for the role and great talent.
Before I get ahead of myself, I understand that there are a LOT of ifs before we even realistically think of him in the first team. He still has to move up to Barca B and I think it just might be possible for next season if he can earn the trust of Vinyals for the remainder of this year as a starter and the B team gets a new coach who appreciates his talent. If Tata noticed Kaptoum when he took over, it's certain that someone like Oscar Garcia would if he became B coach.