Personally, allowing them to wield iron/mithril weapons seems like too drastic a change. I'm not in favor of them being able to have any "extended" contact with iron/mithril.

That said, felar can wield blades of flame, flaming ribs, wavedancers, maces of fire and water, etc. so maybe there's precedent for letting elf/drow do the same.

But I'm still against it. It would neuter the iron/mithril vuln a little too much.