After the iPhone set the pace for what a smartphone is supposed to be like, Android came over and disrupted the market such that established leaders like Symbian were virtually torpedoed out of the market.
This time around Google has Plus, its third major attempt at entering the social space. Though the smartphone market is distinct from the social space, it may not be far fetched to stick one's neck on the line and make the Android claim for Plus.
From how I understand Plus, Google's fundamental goal is to force Facebook to open up so it (Google's) crawlers can access the vast store of user data behind the Facebook walls. And what better way to do this than offer a far superior platform that has everything Facebook and more?
Of course Facebook will not sheepishly open up just like that, something evident from its doing its utmost best to frustrate any attempt at exporting one's "friends" list.
To pull aother Android with Plus, Google would need to iterate faster than Facebook can copy. Not long ago we wrote here about how Google could take on Facebook simply by straddling the latter. Well it seems Google did that and more, so Facebook is the one to now do the straddling, or copying from Plus.
Also Google would need to make Plus as open as possible to as many other social networks as possible. For instance, I should be able to post from my Plus account to Twitter and vice versa. The Liberate your data feature of Plus is already a good sign of how open one can expect Plus to be.
Of course Plus is not even public yet, so it's too early to say what form it will take regarding inter-operability. However, if Google wants to really pull off another Android- which I expect is going to happen with time- in the social realm, it'll first need to make Plus as open as possible, putting the end users in at the center before advertisers.