User blog comment:Kogath/Monster Hunter X Discussion/@comment-26034899-20150909005023/@comment-26034899-20150909214012

Ravenxeo: Well, to each his own. I just thought that it would be great if there was a monster that's on equal terms with you, but now you mention it, the monster would probably be too overpowered if it could use all the items you had. Maybe it would be best if it just used the hunter's weapons and armor instead...

Though I have to agree with you on the programming part. That would be pretty costly, which is probably why Capcom will never add it. But still, characters like Ditto and Shang Tsung were pulled off despite limited technology (though the shape shifting part had to be toned down for the latter due to insufficient memory), so it's not entirely unlikely that Monster Hunter can't make the shape shifter work.