Sometimes when I roll my side, I don't want to roll my main (because I only have time for one account), vise versa, but I do message other users on both accounts. Sometimes when I already rolled my side, I see someone messaged my main, but I can't check it even though I'm online

If linked accounts can share one single message inbox, there won't be any problem like this.

Shared inbox won't validate existing features, such as rollover, because sharing message inbox will only allow users to see and reply to messages sent by other players, and players have to roll at least one of their accounts to see the private message.

It can make playing lioden more convenient. As it is for now, players need to keep track on which message was sent by which account, or simply don't send any message when playing as a side account and wait to message till they play in a main account, and the hassle is not needed at all, as the two accounts are played by one single player, the two accounts should share the same memory (private messages) as the player as well.