I’ve thought about this before. It would be great to have a script that ‘bakes’ actions defined using IK into a FK action. IK is so much faster for creating actions, but currently only FK supports action blending in the game engine. (IK defined actions can be used, but not too sure about constraints.)
My thoughts were to iterate through all actions on an armature and define a new action. This new action would have ‘Rot’ keys inserted for every bone on every frame so the action is then defined entirely using FK. This would result in a very heavy file due to the high number of keys. The keys could then be iterated through and if no change in rotaion is found then all keys except the first key defining a particular rotaion and the last key for that rotation could be removed. This would leave a potentially heavy, but probably manageable action.
Since an action is stored in it’s own data block (I think), it would be trivial to link actions to a different armature, provided all bones effected by the action have identical names in both armatures.
Like I said… I’ve thought about it, and it’s on my todo list, but I’ve not actually done anything on this yet. I think the method that I outlined above should work, though.