Some are really interesting suggestion, but for an online manager game I think substitutions and spreading the tactical options are the only viable options. Other ideas are cool, but kinda not doable for an online manager game where you are not playing the game in "real time" and its a simulation.
I kinda like the OSM as it is, simple yet complicated in its own way. I tried couple more similar games and not one has managed to keep my atention like this one did. So to me personally (and I know lots of people like me), more important part would be to try and keep active and competitive players playing.
Yeah I know those are minority, but they are longterm users. Some guy will see OSM Hall of Fame and spend 1000$ to enter it in a season, but that guy will not be playing the game anymore in 2 months as he will get bored of repetitive play. Thats why I would look into making official competitions run by the game owners (like we had good old OSM World Champioship coupleyears back).
I would also look into making crew competitions organized by the game, also giving crew chances to organize crew tournament "winners cup style" where 32 crew would sign up for a tourney and then played 3 battles in group stage and later continued in knockout.
When we are at crews, crew battle points ranking would be nice since the recent one with medals is a failure and atracts cheaters and bots playing empty leagues..
Anyway, I think competitivity is the key for the future if you want to hold on to active managers who would like to test their skills. Playing simple empty and boring leagues that are not filled with active managers gets repetitive and boring and players who play leagues like that do not play the game for more than a year or 2. Just look at hall of fame, havent checked lately, but couple months back top 100 was filled with people who left the game and are long gone managers who are not active anymore..