I am not sure. The story has still a lot to offer, but I am contemplating, and this is something I started to explain in a past stream, the idea of cutting it into two sets of volumes. 

Like Grey is… is 1-some number of volumes. Then it continues (without a time skip) with a new set under a new similar title or an addition to the original title (yay for Grey is… I can put whatever after lol), and it’ll also be 1-a number of volumes.

Think something like, Little Women and Little Men? or Dragon Ball, Dragon Ball Z?

If I decided to go with this plan, Grey is… will end at volume 7, and I have the ending for that book, a rough idea though.

As for the series as a whole, up until 2015 I had the ending in mind, but while writing volume 5 I decided to drop a main plot point which affected the original ending and I’m just going with the flow at the moment. I’ll have to pick a stopping place at some point, but right now that point isn’t visible yet.