Unless he thinks he can get a waiver to become immediately eligible, it gets him nothing. The NCAA's rule on eligibility is that a player has 5 years to play 4 seasons of his/her sport. Kosi's already been in school 3 years, and played 2 seasons, meaning has 2 years left to play 2 seasons, regardless of whether he transfers or not. So he only has 2 options: transfer to his new school this year and sit out the year, then play 1 season at his new school, or stay on as the backup this year, graduate, and potentially go leave as a grad transfer in 2021 (or maybe win the starting job here).
In other words, his 2 choices are:
2020 - transfer to his new school and sit out the year
2021 - play at his new school
OR
2020 - Canes' backup, graduate in May (or whenever)
2021 - Grad transfer to a new school/compete for the starting job here
Assuming he can't get a waiver, transferring this year would accomplish nothing other than to prevent him from playing in the 2020 season.