Just some ideas from the top of my head.
-Flash light - if used in low light or total darkness gain edge for your attack roll against the illuminated target. Flair compensation negates. Range limitation - Near (possibly use the same rule as with tracers- see below) Mount: under
-Foregrip/C clamp - Gain edge when attacking using full auto mode of fire. This edge has to be used for that attack. ( it could work for burst as well, but I am afraid of it's effects in conjunction with burst fire and anticipation.) Range limitation: Near. Mount: under
-Tracer rounds- If using tracer rounds, grant an edge to every team-mate attacking the same target after your successful attack lasting until your next turn. (single target, careful about bursts and full autos) However enemies which are attacking you afterwords will gain edge. ( tracers are going both ways, you grant your team a trace towards enemies position, but enemies can see from where those tracers are coming from, suggested for Machine gun nests

or situations where you are using range advantage, perhaps sacrificial drones ) No range limitation (note: the word team-mate is not defined in rules, it might actually apply to anyone attacking that particular target, not just team-mates)
-Laser sight should have Range limitation: Near, also having laser sights active could give enemy edge for perception checks and surprise checks (it's easier to spot you). Different modes of laser (low light, thermal) can grant edge only to enemies with matching vision enhancement. Range limitation: Near.
With this in mind, I am thinking that wireless bonus for laser sight could be: you can switch between modes without spending minor action. Finally I am thinking if laser sight bonus would apply for full auto, but I might be nerfing it too hard here.
-Taped mags- Common trick to reduce reloading time, tape two mags together. Useful only for assault rifles and SMGs'. Reloading from 1st to 2nd mag costs Minor action, however than you must use Major action to insert fresh magazine (can be another tapped mags) I would reduce the attack rating by 1 and decrease concealment by 1 (it's easier to spot) not an edge mod, but something which I assume was mentioned in previous editions.
-Extended mags- Increase capacity of the magazine by 10 rounds, doesn't apply for machine guns and shotguns. Decrease concealment by 1. (easier to spot)
-Precision heavy barrel - installed for machine guns and sniper rifles, gain edge when attacking at far and extreme ranges, maybe it doesn't need to be edge, just attack rating boost, which could or could not result in edge gain. Range limitation: Far, Extreme
Considering armour:
-Fire resistance armour mod could negate explosive round damage.
-If you have installed biomonitor in your armour, person performing first aid on you gets and edge to use for that test. Urban explorer jumpsuit is now a cool option. Maybe too cool.

-Flak vest - gain bonus defence rating against grenades and missiles. Reduced capacity
-Buckler- Does not protect against firearms, + 1 defence rating in melee, gain edge when using Block action. ( don't know if it should be limited for Block test or not) Special attack - Damage 3S, AR 4 (or 5). Bucklers are amazing in close combat, they are a good defence/interceptor of incoming attacks as well as for hitting meta humans in the face. Zap versions are possible.