Xfce 4.10 was released in April of this year and uses GTK2 as it's tool-kit rather than the newer GTK3 from GNOME. From the Xfce 4.12 road-map they do have an aim to switch to GTK3 for this next feature release, but it might not happen.
Some developers aren't convinced by GTK3 and there's also limited development resources for converting the GTK2 code-base to GTK3. There may, however, be experimental build support for using GTK3 for those interested.
There were some interesting comments on the topic made earlier this month on the Xfce development list. Additionally, "We would definitely want to see Gnome 3 applets and Unity indicators in Xfce. The problem with the former is that Gnome 2 applets are gone (Mate?) and, as you said, Gnome 3 panel isn't particularly loved either. As for Unity indicators - our main issue with them is poor maintenance. Interfaces are being deprecated more often than we can make releases."
Aside from the GTK3 possibility, other Xfce 4.12 features are still being developed.
In terms of the Xfce 4.12 road-map, the first pre-release is planned for the end of January at which time there will be the feature feeze, the string freeze and "pre2" releaaw in mid-February, "pre3" and the code-freeze in late February, and the Xfce 4.12 final release around mid-March.