I assume you mean open invites can only be sent if the playing sending it is to play first? That would just create a problem similar to IYT - you have to figure out who has to invite who to play certain colours. I don't think anything needs to be changed - Five in Line is even more imbalanced...a proven forced win from the start by player 1 (by move 24 or something like that). If there are invites waiting for the wrong colour, don't accept them.