As you know the 2018 FIFA World Cup preliminary draw will take place on 25 July 2015 in St. Petersburg.
Of course, FIFA have not revealed the seeding criteria, but it could be the FIFA ranking yet again. FIFA have already announced the release dates for 2015. The most recent ranking at the time of the draw will be the July ranking - published on 9 July, while the next ranking would be published on 6 August.
In 2011, the draw took place on 30 July, with the most recent ranking being published 3 days earlier.
FIFA could postpone the draw by 2 weeks or postpone by 1 week and bring the August ranking publishing date forward by 1 week.
Two teams would be the most affected by such a change: Germany and the Netherlands, as their final matches of the 2014 FIFA World Cup would still be include at 100% of their value. In Germany's case only the final (2340 points), while for the Dutch the 3rd place win vs. Brazil and the penalty shoot-out defeat vs. Argentina (3144 points from 2 games).
With the inclusion of these high value games, both teams are pretty much locked in the first pot for the preliminary draw.