While this has a little bit of speculation in it, its well within the realms of possibility. It appears that Dark Imperium is no longer a mandatory stocking item, and there are some possible hints of something new coming soon. This could reset the Sisters of Battle clock.... GW knows (very well at this point), that plastic Sisters would be a huge positive thing to bring in 2018.
Remember that this is speculation at this point........
via an anonymous reader/source here on Faeit 212
In every edition of 40K there has always been a starter set that has
lasted the entire edition (exception is 6-7E which had the same starter
set). The starter set has always been on the list of items that
stockists have to have in their shops at all times. For some reason the
Dark Imperium box is getting taken off this list at the start of the new
year.
No idea why but to me it does seem very strange that the starter box
would no longer be mandatory to stock. So is a new starter box coming?
I do remember there being a rumour very long ago, that came out 6 months
before the genestealer cult was released, that there would be a starter
box featuring the Sisters of Battle vs Unknown.
The Unknown was an army that wasn't in the game yet. So could we be
seeing a Sisters vs Genestealer cult box? There has been some stories
featuring both in the last few months.
Book: Cult of the Warmason: features Sisters of Battle vs Genestealer cult
Short Story: Cast a Hungry Shadow: Genestealer cults features Sisters of Battle vs Genestealer cult +
some CSM that are 3 meter tall for some reason.
So Sisters have received nothing from BL for years (other than mentions
in a book or two) and then 2 stories pop up at almost the same time
featuring Sisters vs Genestealer Cults?
Sisters and Genestealer Cults also have yet to receive their codexes so
there is that as well.
This is all just speculation and wishlisting but regardless it is very
odd that the Dark Imperium box will no longer be mandatory to stock.