It varies. V Collection 8 was for example launched in December 2020.
They tend not to give the public any hints. Thought their recent release of Augmented Brass might be a hint that something is coming.
The next obvious question I guess is, what will they put in V Collection 10, other than Augmented Brass. I think Arturia are struggling now to add more high-profile instruments to their roster from the 'golden age', because the mfrs of the original instruments have their own virtual equivalents and they don't want Arturia competing. Case in point are the two God-level synths from that era which are obviously missing from the Arturia V Collection roster: the Korg M1 and the Roland D50. Both Korg and Roland offer their own virtual versions (Roland through their Cloud service and Korg through a purchasable app) so it seems very unlikely they will licence Arturia to sell a competitive equivalent. Though I''d love to be wrong and for one or both of them to appear in V Collection 10. That would be awesome. But other than those two biggies, there's not much fruit left on the vintage-tree to pick.
Personally I would like to see a replacement for Spark 2, moulded around the same UI/UX as the rest of the V Collection. Spark 2 is so rusty now, it almost creaks when I open it.