The load time coupled with the high sig makes them pretty useless if there's any defense whatsoever. It's like trying to hit a tech with a nuke except 'look hey you get 1-2 shots a couple dozen seconds apart only and don't have 4 sc/lt nailing down the would-be defenders before they can shoot the nukes'. A team with any sense will see the nerve gas coming a mile away and a quick hover over a sector in f7 or a quick tap to f6 reveals when nerve gas sbs are out. Hell I think there might even be an audio prompt.
Against totally undefended bases you still have to sacrifice like 3 players (I don't remember nerve gas sbs being able to use ab) - a SB, a NG SB and someone to get you in and let you set up (or get unreasonably lucky with the high base sig, or be hitting a team with no probage and a very far base in which case your target is either worthless or the team is bad enough to lose to just about anything). If there's no one around to defend on the enemy team, 3 players on a long journey can be a big sacrifice, especially with tac where every defender really counts.
That said NG has its purposes atm. Being able to cap forward tps is very very nice and also easy to set up - especially against exp/tac. Ops are still possible when the team's very distracted... never seen a ng sb used for a recap because honestly what recap doesnt have hvy ints swarming around the exit... coupled with sb's amazingly slow turn speed... Anyways against tech it's pretty weak, especially considering it requires most of the investment (more in money) of a regular sb run, more set-up to deal with the high sig and is downright simple to counter with a little def (the only real risk against a team that isn't camped to nothing is that the actual sbs might kill the base after the ng is shot down).
But raising lifetime to 30s is an interesting change. I think it's also quite a scary one. If people don't notice in that first few seconds (like if other sbs are being eyed) then you could easily fire that missile and if some vet isn't actually looking in f3 instead of boosting at the nearest sb threat in those first 10 seconds or so (where it's obviously something different than an ab on the map) it could easily go missed. The NG sb only has to be eyed for a few seconds - it's possible no one in a position to stop it will even notice this if the distraction is timed well, especially if fighting against sup/tac where reaching the missile is tougher. Have like 4 sbs (or enough that they only need 1 shot off) in a half circle on one side of the base and the NG sb on the other side and it's nearly a guaranteed cap (like a good sb run can be a near guaranteed base kill unless very good defensive scouting), which is kind of op. All it requires is the sbs to let themselves be eyed a little early, but since they only need an ab each for the base shield this isn't a big problem. With very tight timing this could be brutal.
I'd say this is a little too strong, it's also gonna make surprise caps on poorly defended elements too easy, and capturing bases that were just planting would be a joke, though frankly capturing the forward op near your tac is probably a lot more dangerous than killing it
I think toying with the idea of making sbs using nerve indistinguishable from regular sbs instead could be very cool. They're still high sig. They still have to be eyed very early. They still have to get within 800m moving pretty slowly. But it does give them a tiny edge in that with the right sb placement and people being eyed early defenders can be tricked into hitting everyone else first and just giving the NG enough time to hit a tech with its shields down. Difficult, unlikely, but also a lot more useful than what ng is currently and without making it game killing. Cutting down load time 30% instead would also make the numbers seem a lot more plausible (though still really tough) on a marked ng sb.
