I miss galactic challenges

I used to enjoy playing around with my new teams in galactic challenges to get a feel for them and messing around with theory crafting. Since galactic challenges have been removed and replaced with a game mode we cannot use our rosters it has removed something I highly enjoyed doing in this game. Is there a chance we can get galactic challenges back or have coliseum opened up to our rosters? Or please add a game mode me can play around in or sandbox.