Having said that, I am pretty confident that you are not allowed to spend 40 ammo in one action, as OP claims 
It was written much more generically than that. And I don't think it needs to be limited much in order to be balanced....
Multiple Attacks just explain how you resolve it IF you are eligible to take it. Actions themselves need to explicitly mention that you are allowed to combine it with the Multiple Attacks Minor Action. It was the same in 5th edition. Just because an action does not restrict you from using multiple attacks does not automatically mean you can combine it with multiple attacks.
In 6E you are eligible to take the Multiple Attacks Minor Action when you use Wide Burst (attacking two different targets). If you have 4 edge you are also eligible to take Anticipation with this action. This part is clear and not under debate at all. BF in 5th edition also explicitly mentioned that you were allowed to take the Multiple Attack Free Action (but your two targets had to be within medium range).
It seem as if you are also eligible to take the Multiple Attacks Minor Action when you dual wield (attacking two different targets or the same target twice). This can be debated, but Multiple Attacks in relation to dual wield is mentioned in the Off-Hand Attacks section on p. 110 and it is also again referenced in the Multiple Attacks section on pl 111.
If you also have 4 edge, wield 2 firearms and attack two different targets rather than the same target once you are also eligible to take Anticipation while dual wielding (but if you are not ambidextrous you will still split the pool for your offhand).
In addition to this you can also Multiple Attack (but without using a Multiple Attack Minor Action) if you are using Full Auto (attacking multiple targets or the same target by splitting the pool). This part is clear and not under debate at all. This is a change from 5th edition that instead had rules for suppressive fire when using FA firing mode (sort of a frontal AoE cone that attacked both friend and foe).
Note that Multiple Attacks seem to limit this use to either "multiple targets, or you could attempt two attacks against the same target" (which I read as you may only split the pool twice when attacking the same target) and the number of attacks also seem to be restricted to if "ammunition ... allow it" (which I read as if you may only split your pool a maximum of 10 times when attacking multiple targets).
Since you are not using the Multiple Attack Minor Action you are also not eligible for Anticipation.
Unlike 5th edition, Semi Automatic attacks *don't* mention anything about taking the Multiple Attack Minor Action. *Nor* does throwing weapons (Athletics). *Or* Melee (Close Combat). In 5th edition you could use SA to fire on up to 3 different targets as long as they were within medium range. Hence why I proposed a house rule to allow you to fire at two different targets if you are using SA mode.
To take the Multiple Attack Minor Action with throwing weapons or melee weapons it seem as if you need to dual wield (attacking two different targets within reach or the same target twice). In 5th edition they explicitly mentioned that you could take the Multiple Attacks free action.
Having said that, rules as written in 6E are less than crisp and you can probably argue that they can be read in more than one way. But the above reading is the one that makes most sense (especially when comparing the rules in 6E with how they worked in 5th edition).
Also, alternative reading quickly get super crazy (like being eligible to take Anticipation with Full Auto to attack 10 times or even 20 times while dual wielding). There are also no examples that suggest that this is legal. That the outcome seem highly unlikely and there is no supporting examples is often indicators that you are not reading the rules correctly....
But it is your table. Your rules. If you wish to rule that you are allowed to fire 40 bullets with BF mode then you can do that. There is no Shadowrun rule-police that will pin you to the wall if you do. However, you might want to make this reading clear to your players so they are aware.