@YetiMooseA shield as an improvised weapon with the Dual Wielding feat: Does the feat’s +1 AC stack with the shield +2 AC that round? Dual Wielder is meant to work (RAI) with a melee weapon or an equivalent, not something like a shield.
— Jeremy Crawford (@JeremyECrawford) April 15, 2015
@JeremyECrawford Um, you're the one who previously Tweeted that a shield can be used as an Improvised Weapon! How's that not a melee weapon?
— Mark Cronan (@YetiMoose) April 15, 2015
@JeremyECrawford To clarify, around Feb 15 Q: "Must I doff a shield to use it as an improvised weapon? A: "Nope. It's shield-bash time!"
— Mark Cronan (@YetiMoose) April 15, 2015
@YetiMoose Yes, a shield, like many things, can be used as an improvised weapon. This has no bearing on the design intent of Dual Wielder.
— Jeremy Crawford (@JeremyECrawford) April 16, 2015
Unless you get your shield sent to a local guild artisan to make your shield a spiked shield like lizardfolk use. Then it would be a piercing weapon and still have the shield benefits, being able to get you the +3 to AC.