One big challenge in the AFL is getting enough at-bats for hitters, so I doubt they would increase roster sizes. They are already between 35-40 players per team (seven or eight per organization times five supplying organizations).
Perhaps if all of the MLB teams agitated to send more players to the AFL, it would be done. The expenses would surely increase, adding another facility and the related infrastructure.
I think AFL expansion would be more likely if/when MLB expands to 32 teams. Then they could have eight AFL teams staffed by four organizations each. Each system could send nine players plus a taxi squadder. That would maintain the team symmetry and roster sizes would remain the same.
(Today’s structure is six AFL teams, each staffed by five organizations with seven or eight players each.)