Since the traditional bean counters like IDC and Gartner are now in the prediction business, I thought I'll give it a shot.

I'll try the same way I did for the Blu-ray vs. DVD around the time BD won the hidef war against HD-DVD, i.e. beginning of 2008.
Three years later, it turned out, I was much closer to reality than most of the corporate "prophets"...
http://www.satelliteguys.us/hd-dvd-forum/240626-hd-vs-sd-two-years-later.html#post2437109
I will start with the assumption that the iOS vs. Android war in the tablet market will be similar to the war the same players waged in the smartphone market.
But since the number of players in each of these markets it so different, we will look only at the
relative market share between Android and iOS.
According to
this article Android had 1/6 the market share iOS held over the course of 2010.
Some
references claim it was closer to 1/5 by the end of 2010 but we'll see later that this hardly matters.
Around the end of 2009 (if you check
this post) Android had 1/10 of iOS market in September and 1/5 - in December.
And
this post shows the time when Android and iOS had about the same smartphone OS marketshare - November 2010.
In other words, Android jumped from being not more than 1/5 to par with iOS in marketshare
over the course of one year.
Again, we are neither looking at the marketshare numbers per-se (only relative), nor taking into account other players regardless of their share and role.
I assume that both, Google and Apple, will "fight" in the tablet market the same way they did in the smartphone and their
relative dynamics will be comparable.
I think one correction is needed.
I believe Apple realizes that they can't be as "greedy" in the tablet market as they were in the smartphone (much less of a must-have item) and will sell their tablets at a lower profit margin. Also, Google will have a harder time to keep their partners happy and both those factors will
double the chase time (I know, very un-scientific).
Bottom line, based on what is outlined above, here is my prediction: not later than in two years,
1Q 2013, Android and iOS will have about the same tablet OS market share.
I don't know what that share will be and whether any of the two will be the leader - my claim is that they will be on par.
Will see what happens...
Diogen.