If you think of the most common uses of gif, its probably the case that such a datatype would be pointless.
Image formats that are used for large, detailed images benefit from the horsepower. As you go down the data size / decoding complexity scale though, context switching alone probably becomes the dominant factor.
For images below a certain size for "simple" formats like gif (which let's face it, is used a lot for small images) flushing the datacache of your PPC and 68K likely involves moving more data than decoding this smiley :-D for example. In such cases, it would actually be slower to call the PPC than just do it on the 68K.
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In my opinion, smart datatypes for WarpUP / PowerUP should estimate the output data size and use a PPC or 68K decoder depending on that. There could even be a preference setting to determine that threshold, rather than hard coding anything.
