I definitely like the idea of adding second teams, but honestly I don't think the utopia/separate world or U18 teams sound fun at all. I doubt those systems would last long.
The U18 team idea gives too much benefits to supporters if they are allow to develop players for transfer to their primary teams. Anyway, if you only have the players for a limited amount of seasons, then it's not as fun to train them and develop them into interesting builds. And, you remove a strong connection between the user and their team, of being able to follow a group of players as they play and win together for a number of seasons.
The utopia idea just sounds incredibly boring to me. I want players on my second team who have real flags, real names, can make it to U21/NT. Removing that removes a huge draw of interest from me (though, I do support the rule that no secondary team can represent a country in BBB). Another issue is how the transfer market in Utopia would work. With much fewer teams, and presumably no players allowed to be transferred between regular BB and utopia (the utopia players don't have countries that correspond to regular BB world), the market will not work nearly as well. And, would utopia start with all low skilled players, the way BB did? That means it will take a few seasons for players to develop into solid players. Also, none of this mentions the infrastructure needed to create this second BB world.
However, I am somewhat sensitive to peoples' concerns that lower division teams might get overwhelmed by strong managers with second teams. For that reason, I really like the idea of reducing, or removing, the new team bonus money normally given out.