This is an interesting theory. It could also explain why the dogs alerted to Cuddlecat (the toy). I remember an interview with KM where she Said that MM would never go anywhere without Cuddlecat. If MM woke up and went to her parents room, she could have broght the toy with her.
To me, it is also an interesting thought that if this is what happened the perp may not had broken into the appartment with any other intentions than to burgle it, he may not even had known that the children were there.
He may have paniced, but her in the closed initially while trying to figure out what to do/clean any traces he might have left, and then ultimately decided it was better/less risky to take her with him, putting the toy back on her bed for some reason.
What I cannot fit into this theory is the evidence that German LE claim to have of her dead and and how she died. Hr. Wolthers speaks about this very confidently, making me think that is must be something he has seen with his Owen eyes, like a photo/video, but I may be wrong in my interpretation of this evidence.
With all the theories being discussed about abuse, Dark web and snuff videos, I kind of hope the accidental(?) suffocating her in the appartment is what happened, for the sake of Madeleine and her parents.