Decay:
Strength: Widely believed and follows the forgetting curve's theory as well.
Limitation: Does not explain how some people have vivid memories of things they haven't thought about in years, while we can easily forget information from a recent date such as yesterday.
Interference:
Strength: Helps explain why we forget information that is similarly linked in it's type and form. (eg: phone numbers)
Limitation: Task similarity is seemingly needed for interference to occur in it's retrieval.
Motivated:
Strength: Supports understanding of why we are unable to remember particularly distressing moments.
Limitation: Applies to very limited situations.
Retrieval Failure:
Strength: Helps us understand why we are sometimes unable to remember the information, even though we 'know it'. (T.O.T)
Limitation:-:
Basically, each forgetting theory supports each other, and although all of them aren't considered perfect, they each provide an insight as to why we possibly forget information, and is thus valuable.
I never heard of a question that concentrates on the limitations of these theories. More so the concepts and the tidbits within.