Currently have 10 gb and in the future maybe in 2033 have 20 or 24 gb
Check this. 7 GB growth in the last 12 months.
http://blockchain.info/charts/blocks-sizeAt this rate, 20 GB will be in 2015 or 2014. Someone bringing a new full client online could take days - header only clients will increase in popularity as the block chain grows.
At least the rate of growth seems to be constant.