This patch is very incomplete, and probably won't pass the 'make test'.
It did for me, but that's not saying much. The current IPicture-based loading is quite broken.
wine-staging contains a pretty full and well tested patch that reimplements metafile loading in gdiplus using gdi32 APis: https://github.com/wine-compholio/wine-staging/blob/master/patches/oleaut32-... it should be possible to either use it directly or as a base for your work. There are some other related patches in staging that touch the metafile loading in gdiplus.
Yes, that looks better than my version of emf loading. Would you be willing to send it to wine-patches?