You guys need to follow Mearls patreon so you can see the actual design instead of speculating about things he is actively trying to solve.
Let's look at
@mearls new designs.
Each Class has a class aciton, like a Fighter Action or a Cleric Action. These actions are actually menus.
The Fighter action may look something like
- Make an attack
- Make an ability check
- Use an item
And you pick two of these options.
If something were to modify this, say a Paladin's smite, it joins the menu.
+
Paladin's Smite. When you take your Paladin action, you can spend a spell slot to gain the following option: Make a special attack.
Hit: Deal a bonus number of d8 radiant damage dice equal to the level of the spell slot you spent on the smite.
Note Mearls doesn't have this exact option, I created one so as to keep his Patreon content on his Patreon.
The idea is that your Menu expands, you gain different Menus, and sometimes you gain a rider to Menu options instead of a brand new Menu option. So Dual Wielding would be either an option under a menu or a special Dual Wielding Action: Make an attack with a weapon in your mainhand and a weapon in your offhand. The offhand attack doesn't add your Ability Score modifier to the damage roll.
The idea is to have easy buttons and then buttons that access action pools for combat. It would, ideally, make things easier for a player to navigate and easier to design new features in this system.