Many linear predictions, here is another based on forum data:
2010 new members : 1 to 700 -> 1$
2011 new members : 800 to 14000 -> 25$
2012 new members : 2000 to 3000 -> 7$
2013 new members : 2000 to 30.000 -> 121$
2014 new members : 17.000 to 46.000 (so far) -> 650$
simplified:
2010 new members : to 1000 -> 1$
2011 new members : to 10.000 -> 25$
2012 new members : to 3000 -> 7$
2013 new members : to 30.000 -> 121$
2014 new members : to 50.000 (so far) -> 650$
1000 to 50.000 in 5 years. 1 to 650
50.000 to 2.500.000 in next 5 year. 5 times as many members -> 16.250$ per coin in 2019
Assuming linear scale 10.000$ in ~3.5 years. around 2016-2018
Ah and in 2030?
I think it makes more sense to compare it with other technologies and the rate of adoption (compare to supply of money - M0 or M1 of the world).
M1 is worldwide about 35 trill. USD. If every transaction has one part in Bitcoin, and there would be a 100% reserve (coinbase has all coins it should have), we would get 1 750 000$.
More realistic would be, that every 20th transaction is in Bitcoin (5%) with a 50% fractional reserve which makes it 40 000$.
To that the value of Bitcoin decrease if it is volatile and not the legal tender and you can't pay taxes with it. The value would be higher if it has other values like small transaction fees or good store of value.
The growth of the internet:
1995 there were 16mio. users. This was 0.4% of the world population. Is Bitcoin already in that stage? I don't think so. There are less.
Until 2000 this number doubled every year.
Until 2005 it was 25% every year.
Until 2012 about 10% every year.
http://www.internetworldstats.com/emarketing.htmSo, but we need to get to the 5% adoption rate. This was around the early 2000. So let's say in 5 years every 20th transaction in the world is with Bitcoin with 50% reserve.
On the other hand the price of the internet related firms was not the same like the real adoption. Remember that dotcom bubble. It is highly possible, that there will be a big hype about Bitcoin and it could be worth a million USD - for a very short time.