In a word: yes. In a few more words: yes, and the future is already here. In a lot of words:
When people ask "Is (product/service/phenomenon) the future?" they usually mean to imply that there is a boundary to be crossed, past which things will no longer be the same as they once were. A classic example: Is VHS the future? Yes, it certainly turned out to be, because for those of you who may be too young to remember, VHS and Betamax were in a video cassette format war, and VHS came out on top, much in the same way that Blu-ray has ousted HD DVD as the new hi-def disc of choice.
However, in the context of online gaming, there is no either/or choice to make. Rather, what we're seeing is a simple add-on to the games that already exist. So instead, what's being asked here is probably "Will every future game be played online?" And the answer to that is ... maybe.