Bioware has already confirmed that Mass Effect 4 is going to come out with an online feature. The game developer mentioned that the online gameplay will allow players to get together and enjoy the new Mass Effect world.
Well, Mass Effect lovers need not worry much about it as the online gameplay will only be offered in a separate mode and it won’t affect the single player mode.
This is obvious if fans are to check out Dragon Age Inquisition. The latter basically came out with an online mode being offered in a separate tab. It has nothing to do with the single player gameplay. Besides, both the Dragon Age Series and Mass Effect series share a lot of similarities hence this confirms that the online gameplay for Mass Effect 4 is going to be more like the one in Inquisition.
To sum it up in simpler terms, the online gameplay coming to Mass Effect 4 will just be an added bonus or an extra mode. The game will still be centred on the single player plot.