Here are some very easy things to add.

Currently there are 4 types of splines Spline, Linear, Constant and Spline Break.  I would like a fifth one which would be Spline AB.  It would only create a spline curve between points A & B.  If I add another keyframe after point B then it would be a spline Curve from B to C.  That way you will never have the over shoot caused by putting a third point in that is not on the natural curve of the spline.  It would in effect be like putting in a Keyframe Spline and one frame later a break spline.

Also I would like to be able to set a default type of spline to be used instead of having to go in and change it after the fact.  A simple check box in front of each type and use the one that is checked until some other option is selected.

On the layers be able to select which objects that I want to be effected.  So I would like to have a layer that has just lights.  If I  am not on the light layer then any changes I make to the lights will not be recorded.  Should have a warning saying I am not on a layer that allows the changing of the lights.  Or better yet if I select a light then if there is only a single layer for the lights auto switch to that layer, if there are multiple layers then present a choice of which light layer I want. 

Also on the layers if I have three assigned to Rex it would be nice to be able to select which parts are in the selection choices.  Most of the time I do not need to animate the scales on a joint so would like to have a way to have them not show up in a layer if they are not part of the layers selected options.  So I may have two layers with no scale graphs and the third one may be set to just the scales if I wanted.

Most of the above should be fairly easy to create using a plugin since the fuctions they call are available via Python.  Or at least as I understand the functions listed in the Python manuel.  The following will be a bit harder since I do not know if you can get the information needed since I can not find a Python listed function for them.

The IK chain:  Is really only a problem if you are trying to make a animation longer then a couple of seconds.  In a real work flow each scene should be limited to what action is required for that sceen and nothing else.  and each scene complied in a video editor.  With proper planning and storyboarding you should be able to create a scene with IK on then another with it off as the action dictates.  Haveing said that It would be nice to have a graph of what the joints that are effected by IK are doing during any point of the motion and it would be even nicer to be able to step in and make a tweek to the motion to make it do what I want it to do at any moment.

As far as the foot sliding in imported BVH files the easiest way to handle that is to remove/suppress/enhance the XYZ motions of the Hip actor.  Import your BVH file then go to the layer that has the Hip xTran/yTran/ZTran and either clear them in which case your figure will be walking in place or modify the frames to make the hip move the amount required to make the foot fall and stay in place till the next foot falls.  A little bit of effort but makes for a nice clean effect.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13