There was no such thing as a G5 rep in the 4 team format, you just had to be ranked in the top 4. Boise would’ve had to be undefeated and have quite a few things go their way to make the playoff in a 4 team format, just like Cincy that one year.
I actually think in this hypothetical they would’ve had those things go their way this year if they had gone undefeated. They would’ve had a nice Oregon win on the road like Cincy did at ND that year. Also the teams, aside from Oregon with 1 loss, they were competing with for the 4 spots all have 2 losses while Boise would’ve been undefeated, again just like Cincy that year.
Even if they change the format (up in the air atm) in 2026, teams from the G5 will most likely have a representative in the playoffs.