As always, the Cool VL Viewer is the first TPV to implement LL's latest (pre-)released feature. Today, it's Bento skeleton avatar (AKA avatar v2.0), which made its way to the experimental branch of the Cool VL Viewer.
For full details about the Bento project, please see
LL's corresponding knowledge base article. See also the
project Bento testing Wiki article for how and where to test Bento, and for sample meshes and anims (remember that in order to upload "*.anim" files, you need to use the "Bulk upload" feature, not the "Animation upload" which can only deal with "*.bvh" files).
Should the need arise, you may toggle the rigging to the new skeleton bones/joints via the "Advanced" -> "Rendering" -> "Enhanced skeleton rigging" entry (any change to it is effective after a viewer restart, which you get alerted about by the viewer).
In the Cool VL Viewer, the joints debug display is obtained by checking the "Advanced" -> "Character" -> "Character debugging" -> "Show Avatar Joints".
For the detach pie menu (right click on your avatar, "Take Off >" and "Detach >"), the new joints have been integrated to the existing joints sub-pies (unlike what LL did for their viewer, which will confuse the Hell out of future SL residents: how would they know what joint was a legacy avatar joint and what other joint pertains to the "Enhanced" avatar ?...), with two new sub-pies added: one for the extra head joints (the first "Head" sub-pie being already full !), and one for the extra limbs (tail, wings). Note that the hands, which used to occupy a pie slice at the highest level, have been moved to the corresponding Arm (left or right) sub-pie, and that, to make room for the new "Groin" joint in the "Torso" sub-pie, the "Root" joint was moved to the "More limbs" new sub-pie.
The "Make New Outfit" floater has also been rewritten so to be able to take the new joints (and any future joint/clothing layer that LL could still have is stock for us) into account.
Note that, for now, you can only upload Bento-joints rigged meshes on the SL beta grid (Aditi); given the Bento avatars crash some viewers

(not the Cool VL Viewer, not even the long-deprecated versions, since my "paranoia" caused me to put the necessary safe guards in its code ages ago), you should not expect to see this feature hitting the main grid too soon (at least not until the most widespread TPV got it fixed and its users forced to upgrade)...