Getting back to two weapon fighting
The thing that bothers me is that the D&D idea of two weapon fighting (an extra weapon = an extra attack, although perhaps at a penalty to hit, depending on the edition) is NOT how two weapon fighting works in the real world.
The main goal of having two weapons was to have more options, more range (a long blade for more distant work, a shorter one for closed in range) and for defense (parry with one blade, strike with the other). It wasn't to attack twice as fast. Warhammer 2nd ed, for its imperfection, had a much more realistic take on two weapon fighting than D&D....
Getting back to two weapon fighting
The thing that bothers me is that the D&D idea of two weapon fighting (an extra weapon = an extra attack, although perhaps at a penalty to hit, depending on the edition) is NOT how two weapon fighting works in the real world.
The main goal of having two weapons was to have more options, more range (a long blade for more distant work, a shorter one for closed in range) and for defense (parry with one blade, strike with the other). It wasn't to attack twice as fast. Warhammer 2nd ed, for its imperfection, had a much more realistic take on two weapon fighting than D&D....
What did Warhammer do?
I second the vote for interest in how Warhammer did it.
I am in the minority, and am inclined to keep it as a bonus action.
I understand the drawbacks, but look at them more as tradeoffs for versatility. IMO.
Well, for Strength users, at least. There are no light, finesse simple weapons in core, so a Dex dual-wielder would be limited to 2d4.I agree. I think a lot of the people are just looking at the "specialized two weapon fighter" case and ignoring the other cases.
Like adding the damage together - means that any simple weapon wielder wanting to use both hands an Attack action goes from d8 (greatclub or versatile staff) to 2d6 (two of many d6 weapons) - now equal to the very best two handed martial damage.
Everyone, please evaluate how your proposed solutions will affect the non melee-focused cases like clerics, non-valor/sword bards, etc. If it makes it a no brainer to always use two weapons, that's not a viable solution.
That being said, that's one of the reasons I've never liked the "add the weapon's damage" together approach. It also doesn't give the feel of making more attacks (an important aspect to retain, per Mearls discussing survey responses), and it interacts oddly with weapon buffs and magic weapons.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.