IK implementation

Hi there!

I have a couple questions/comments about the inverse kinematics system in Blender. I have somewhat of an atypical use case in animating mechanisms: each joint is limited to a single degree of freedom (which is a little confusing to set up, since IK solutions are not constrained by the pose transform locks, but only by IK-specific orientation locks).

Mainly, I’m curious why IK is limited to armatures and not trees of objects and their parents. It is much easier (for me) to set up a chain of links in object mode through parenting, and it would be amazing to apply IK to those chains rather than through armatures.

I get the feeling that there is some intent to implement IK for object trees, since the option is available in the object constraints but only reports an error at this point. I would think that if IK will only ever work for bones, that option would not be shown in the object constraints menu just as a matter of usability.

Also, prismatic joints can be hacked together using track constraints, but it would sure be nice to use prismatics in IK chains.