[Bf-animsys] Feature request to NLA editor

[Anna]

Hello, developers,
I have a proposal, to make a very small addon to NLA editor, that is going to be extremely useful, to my mind. 
As you might know, some animators greatly lack "animation layers" in Blender. NLA editor is supposed to resemble work with animation layers with actions and poses. It has 4 modes: Replace, Add, Substract and Multiply. However with these modes you cannot act in a classical "layer" way. That is, you cannot position (rotate) a bone in NLATrack.001 situated above NLATrack (see .blend file attached), and expect it to preserve this exact pose (from NLATrack.001) over animation played in NLATrack. Because this very pose snaps from its position according to calculations made by a chosen blend mode (Add, Miltiply or Substract).
So my proposal is to make a kind of new "OFFSET" mode, that will make calculations of a difference between NLATrack.001 and NLATrack and keep this difference over the whole animation. So you will be able to insert exact poses over existing animation. Moreover, it will be possible to change this pose influence via "animated influence" menu (set Zero-keys, for example). And all this will be what animation layers do exactly. 
Sorry, if I do not understand NLA system workflow somehow, or if I am repeating an old idea, or if this thread already exists somewhere. I looked through animation feature requests and to-do lists and made some inquiries at blenderartists.org - this seems to be an open question still. 

File .blend link:
http://www.pasteall.org/blend/40964 

Regards,
Anna
PS: Attached file has an NLATrack with animation. It has a "BalletPose" in Poselib and this pose is inserted into NLATrack.001, placed over NLATrack in NLA editor, with animated influence. I cannot set this exact pose in the beginning of animation, because there is no such mode in NLA editor. It just starts to calculate either Add, or Miltiply or Substract, which is not desired in this case.
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