How can you say hat the maximum difficulty is reached ?
Economic considerations (equilibrium):
Let's take the following example:
A Zeus X6 (20 MH/s) costs + 1 year electricity costs about 940$ (if you are lucky, assuming 0.1 USD per kW/h); in fact most people will pay significantly more for it (VAT, transportation, higher electricity costs etc. will probably mean that most people will effectively pay about >1200$),
In 2014 approximately 5.256 million LTC will be mined, assuming 5.4 USD per LTC, that means 28.3 mn USD.
To cover your cost of 940$ your miner should make a share of 0.003312% of the total pie (otherwise you will mine at a loss)
If this is the case the total hashrate should never be higher than 600 GH/s = 20 MH/s / 0.003312%.
Now take into account that large buyers, manufactuers etc. will get a discount and do not pay 940$ for the package, but rather 700$, then you arrive at an equilibrium level of 810 GH/s.
In other words, no one with a sane mind will invest in a X6 for these prices given the difficulty / LTC price. Thus it is rather unlikely that the hashrate will grow much higher than 800-900 GH/s unless new hardware is available or the LTC price increases again.
https://bitcoinwisdom.com/litecoin/difficulty