We will also eventually need to store region objects in metafiles. The way paths are stored in metafile regions looks identical to GetRegionData.
AFAICT the metafile format for regions is the same as GetRegionData, except that GetRegionData has additional headers.
I think that ideally we should be sharing code for serializing these object types. I don't think that going through the GdipGetRegionData API is necessarily the way to do it though.