This is one of the big things that beta testers have been discussing, although it'd be silly not to consider non-supporter input. Here's the list I compiled regarding possible changes in order to balance out Ammochain:
- Apply no-ammo to targeted enemies only
--- Apply no-ammo to chainfire attacks only
--- Allow for chainfire to persist as you move (full -> warming -> initial per step, firing increases as normal)
- Ammo is infinite but reloading is required
- Ammo is finite but reloading is not required
- Ammo cost is reduced (somehow)
- Increase ammo capacity per inventory space
- Alter the prereqs/blocks on MAc
--- Blocks: Remove SoG, add HR/Iro
--- Prereqs: Remove WK/(SoB/Fin), add Rel/TH
This is by no means a full list of possibilities, but it's something to get the mind going.
As far as MAc works as a whole, even now, it's hard to make use of it in a N! game (sans AoMC). You get no defensive traits for it, no Int, and infinite ammo really isn't all that useful when you have respawning ammo carriers. For easier difficulties (say HMP or UV), it's still hard to get going but the payoff is well worth it, especially since you can spray into the dark and kill a decent amount that way. MAc becomes less useful on harder difficulties, where getting ammo becomes less and less of a problem, whereas killing enemies quickly is more and more important (and so EE would be a nice trait).
Another big consequence of MAc, however, is that you don't have to carry ANY ammo, save some rockets, and still blow through the game as normal. Plenty of space for spare armor, med-packs, even consumables you'd normally not have room for. This is potentially more important than the infinite ammo itself, and so I believe that any balancing should reflect this part moreso.
I don't know for sure, but guessing from how he talks about MAc is sounds like Const has used it only on the easiest difficulties (ITYTD/HNTR). And yeah, it's pretty much a win button there. You'd be surprised how much lacking accuracy can bite you back though. I can tell you that Ammochain does NOT shine against multiple enemies because of this...at least when multiple enemies are visible at the same time. Unless we're talking about a horde (and really, why would you set yourself up like that) reloading is rarely a problem once your traits are in order. Furthermore, a quick trait addition (Fin -> Jug) will allow you double capacity at no extra time, and if 80 cells aren't enough to handle a rough situation, I don't know what is.