For the Wayland 1.13 release candidate it actually doesn't have any changes over the earlier Wayland 1.13 beta. While there's been a fair number of improvements since Wayland 1.12, nothing landed since the beta release last week.
Then there is the Weston 2.0 release candidate. There are a ton of changes as usual for this next feature update to Weston; the bump to v2.0 is happening rather than v1.13 due to the new output configuration API breaking the ABI. Landing since the Weston 2.0 beta is an improved XWayland warning message, a few DRM compositor fixes, and other basic work.
Look for Wayland 1.13 and Weston 2.0 to be released around 21 February.