Hey Oleg!
Thanks for this important bit. I was just struggling with exactly this problem, although I had synchronized my kits earlier today. However, I had to add the ~amd64 so that emerge finally picked it up. Perhaps the samba target should be updated to refer to >docbook-xsl-stylesheets-1.79.1-r1 in their dependencies?
I'm so glad it unblocked the upgrade... I took a loonnnng time to finally converge to a full working build on kits. Looking forward to reaping the benefits!