Idk if this would be a good idea or not but how about an inventory bar for any unused units?
I mean it's not really realistic but it does keep unused unit's in an area so you can place needed unit's in available bays.
Yes this could be abused and have tons of units in there so you don't have to spend but this could also be handled say if we got 5 slots or so and could buy additional slots via Coins which could benefit Sebastian financially. Like 5 coins per slot and you know there will be players wanting this and would buy tons of coins for it.
Again to keep this from being further exploited there could be a limit as to how many slots we would be allowed.
I don't know guys, Tgis idea was thrown in the air out of nowhere so I figured why not drop it on here and get everyone's opinions.