We'd nominally like to have OpenRefine 3.9 released in October, given that 3.8 was released at the end of April and we're targeting a 6 month cadence. I had hoped to have the release process underway by now, but life has intervened. I'll be travelling for the next couple of weeks with, perhaps, intermittent connectivity, so I'm going to target releasing an initial beta the second week of October and hope to have the final release out about a month later in mid-November. This is perhaps optimistic given that the 3.8 beta process took two months, but we'll use it as a target for now.
I've started populating the 3.9 milestone on Github. Please feel free to suggest modifications (additions or subtractions) to that list of issues, particularly if you have work in progress that you think is close enough to complete to include.
Best regards,
Tom