Multiple Attacks also explicitly lets you mix and match different weapons, skills, firing modes.
I don't see an issue with a character holding a firearm (such as a pistol or SMG) in one hand and a melee weapon in the other (for example a combat knife).
With a multiple attacks minor action he would then be allowed to attack with both at the same time. For example a wide burst attack with the SMG and at the same time performing a melee attack with the combat knife.
There isn't an issue with different weapons, the issue is the implication that a single Major Action (Attack) plus Minor Action (Multiple Attacks) is allowing you to to make two or more Major Action (Attacks), albeit with a reduced dice pool. Edge Actions like Shank, Knockout Blow, Anticipate, different Firing Modes have an assortment of restrictions on them and it's up to the GM to sort that out. And, yes, any given table can sort out something that works, as these threads have shown, it's up for debate as to what is the most correct. Or least wrong.
My own simple preference would be to do a Wide Burst with an SMG and a melee attack with a combat knife would be that it cost two Major Actions. Which is an option. Personally I've rarely seen players split dice pools. I suspect in 6E the majority of the time anyone is using the Multiple Attacks action it will be in combination with Anticipate or some other attack option.
House Rules discussion Attacking with two weapons is a +2 AR.
Mm..... What if you are wielding two different type of weapons?
(what DV and AR value would you use in that case and what if one is set to Full Auto while the other is set to Burst Fire...)
Primary weapon (as decided by the Attacker), and any Firing Mode or Edge Actions, gets +2 AR. Secondary weapon is, essentially, cosmetic. Attacking the same, or different, targets with each weapon (or one weapon twice) can be done with two Major Actions. Both getting a +2 AR.
I kinda like the idea that if you wield two weapons (or if you have two readied throwing knives or shurikens) then you are suddenly allowed to attack the same target twice (by splitting the pool and spending a multiple attacks minor action).
That the only other option if you wish to attack the same target twice (with a single weapon) is to use a firearm set to full auto (trading 6 AP for a minor action)
Splitting dice pools happens so rarely in game, I don't think eliminating the Multiple Attack Acton is taking a meaningful option away from the players. There are still AoEs, Firing Modes and then (House ruled) Edge Actions to give players multi-target options.
Like I said above, I suspect a majority of the time players will be using the Multiple Attack Action in combination with some other combat option. I'd skip the middle man and give the players a well defined pre-bundled option. YMMV.