Right there. It is not the intended rule.
Yeah, like I said above in my post. The Devs have stated that (despite it being OK in RAW) the
intent of dual weilder was for it not to apply to improvised weapons. I agree with you that this is the only point of contention.
By RAW (and RAI):
1) If I have a shield at hand, I can use it as an improvised weapon.
2) I am not proficient in this attack unless I am proficient in improvised weapons.
3) Assuming the only thing I hold is the shield, and I hold it in one hand only, I can obtain Dueling F/S's +2 to damage with the shield if I use it as a weapon.
4) If I bash someone with the shield it deals 1d4+Str damage (like any improvised weapon)
5) If I am a Paladin I can smite evil with my shield If I use it as a weapon.
6) Even if I bash someone with my shield as an improvised weapon, I retain the +2 to AC.
All good so far.
The question is re: TWF with the shield.
Improvised weapons do not (by default) have the 'light' property. Thus it is impossible to TWF with improvised weapons
unless the DM attributes the 'light' property to the weapon; which he is perfectly entitled to do via RAW for smaller improvised weapons. RAW lets a DM give a broken bottle the same stats as a dagger - making a broken bottle a finesse + light improvised weapon, or allows him to grant a 10' long ladder 'reach' or grant a 5' long crowbar the 'heavy' quality. And so forth.
So by RAW, yes you can TWF with two improvised weapons (as long as the DM awards them the 'light' property).
An example would be two sharpened toothbrushes (shivs). Yes you can TWF with those improvised weapons (as long as the DM agrees they qualify as 'light').
The only issue in dispute is the Dual Weilder feat. The Devs have stated (for some reason i dont understand) that the Feat was not designed to be used with improvised weapons. It's got me stuffed why seeing as this ruling is inconsistent with every other ruling on the topic of 'what counts as a weapon'.
Although RAW and consistent with prior rulings, the feat
should apply to improvised weapons, the Devs have stated it wasnt intended to be used that way, and then leave it as a DMs call.
There is
nothing in RAW that stops a PC from using a shield as an off hand weapons (assuming he has taken the Dual Weilder feat). The Devs may not have meant it to work that way, but RAW doesnt reflect that.
RAI maybe, but ultimately its up to a DMs call. Aint nothing broken with it, so I certainly allow it.