Lignite / brown coal is generally suitable for CTL. The type and composition of coal will affect it efficiency in the process, the need for and type of additives etc. I anticipate that currently BLK is in the process of (a) proving up its further resources and (b) having them sampled for the best process and conversion rate etc. At that stage we will have a clearer idea (it already has proven resources to a far greater extent than several others ...).
Depending on the type and composition of coal, a break even oil price of between about US$25 - 60bl is required. So, the GTL cos should be okay, the issue (for those that actually establish plants) is the level of profitability.
At the risk of being obvious and tedious, below is a small selection of links. You will see, eg the second link, that Texas may have its hayday again on lignite to crude conversion. Needless to say, techologies are advancing all the time. My sentiment is very bullish.