In my ḍād package (for Arabic typesetting, see also the TUGboat paper) I use a PostScript font with OFM metrics file. I load the font in the usual way, going through an FD file. This works only for luaLaTeX, since the latter is the only OFM-compatible TeX offspring (thanks to its Omega genes).
My ḍād font is not loaded anymore when I include the fontspec package. As you can see if you visit this overleaf page, as soon as the fontspec package is loaded, the OFM-PFB font dad cannot be found anymore. This means that a user of ḍād cannot use TrueType fonts in luaLaTeX (at least not going through fontspec, which is the most practical way), and this is quite a pity.
Does someone know how to load a PFB font with OFM metrics in a fontspec-compatible way?