The algorithm in the bitcoin network adjusts difficulty to match the hashing power, so that on average every 10 minutes one block gets mined.
6 blocks per hour corresponds to 2016 blocks per two weeks.
The difficulty increase depends on the hashing power added during the previous two weeks 2016 blocks. It is impossible to predict the difficulty increase using just technical analysis. A better estimate would be to take the current wave of ASICs in the delivery pipeline and add their hashing power to the total hashing power curve. However, it's hard to guess when they will be delivered and how fast they will be activated.

Onkel Paul