There are going to be a lot codex releases between now and the end of the year, , so keeping an eye on what is moving to no longer available may be a small clue to new models or repackaging coming soon. Here is something seen last night regarding Grey Knights.
While at this point we know Grey Knights are in the upcoming line up, we don't yet have a solid release date.
via a reader in Faeit 212
I saw something last night on the GW site that I thought might be of interest. In the 40k store all the grey knight boxes are 'no longer available' possible indication of new knight models on the way? The land raider redeemer is also 'no longer available' but don't know what this could mean as the standard land raider is just saying out of stock.