Admittedly I haven't attempted a mod of this scale since Oblivion, and I never released that, but I currently have plenty of free time, and likely will for a while, so, I'm starting some pre-development and script writing work on a Gunners faction mod. The idea is to stick to vanilla assets as much as possible, but to create a faction that will at least include the option to be a 'bad guy'.
Development notes, really interested in feedback.
No major changes needed
Add a Gunners specific quest for just after the Brotherhood shows up. Second Gunners quest overall.
Hunter/Hunted - Add extra radio dialogue and make Gunners friendly/helpful if part of faction. Possible orders to terminate K1-98.
The Molecular Level - Add option to build Teleporter at a Gunners base, requires a mechanic character and a settlement area.
New set of quests leading up to "The Nuclear Option" Should include neutralizing Minutemen and Brotherhood before Institute. Railroad poses no real threat to Gunners. Potentially integrate submarine to destroy Prydwen, Assassinate Preston, Sturges, destroy The Castle if "Taking Independence" is completed, kill Ronnie Shaw if "Old Guns" is completed.
Quests regarding Institute will be passive, essentially just "do what father says and report." Will go until Beryllium Agitator is to be retrieved, then report and somehow sabotage it after getting it.
1. Recruiter shows up after killing so many Gunners.
2. Opportunity to help Gunners, possibly over radio
3. Recruiter in Goodneighbor
4. Injured Gunner tasks you with completing his job, for a cut.
5. Use an existing quest involving Gunners
Faction Side Quests
Will involve settling a power struggle. At least 5 quests. Two choices of leaders, one (Captain Bridget? ) will cull the existing Gunners ranks of ex-raiders (Tessa, Baker, Ryder, and Clint will all go, along with everyone at the Mass Pike Interchange and Hub City Auto Wreckers) and return to more moral, but still mercenary roots. Some Gunners locations would be filled in with other enemies (Raiders, Ghouls, Super Mutants), due to reduced ranks. MacCready may be willing to join you after this.
The other (Captain Wes?) will cull the "Old Blood" and embrace the purely 'for profit' standing of the current Gunners. Will only involve two or three officers and their loyalists, probably at the two Vaults (75 and 95).
If siding with the old blood, the Brotherhood and Institute will still be destroyed, but the Minutemen will be left alone. If no side quests are completed the existing leadership remains for Main Quest, can be turned around afterword.
Will be similar to Minutemen, but no real concern about letting people evacuate. Agitator will already be sabotaged, strike will be focused on retrieving tech before it blows.
Early-Unique combat armor upgrades, or armor upgrades in general (apply skull insignia), discount from Dreth
Late-???? possibly something with vertibirds
There are several occasions throughout the game where other factions' activities could be reported to Gunners leadership. Definitely report on Institute technology throughout.
Kid in a Fridge-Option to help Bullet, Possibly add faction specific option to talk down Bullet
The Devil's Due- Potential integration as a side quest, or joining quest.
Atom Cats-option to talk down the Gunner's attacking, or turn on Atom Cats, possibly change Gunners to standard raiders
HaluciGen, Inc.- Possible integration as a side quest or joining quest
Ness- Gunners won't side with her if you are a member
MacCready will refuse to join, or even talk much if you are a member of the Gunners. Barnes and Winlock ignore you (disable most dialogue)
Long Term/Low Priority
Possibility to kill Preston and his party at any point (would end minutemen quest line) + Jewel of the Commonwealth alternate quest giver for killing the group, perhaps a note referencing Valentine
3 types of repeatable and/or radiant quests, possibly extorting some of the settlements that have settlers by default
Gunners insignia skins for Automatrons
Companion unique to Gunners with own questline.
Rerecord Captain Wes' old lines to match new voice (if used)
Make Gunners Plaza more of a settlement/fort, refine daily schedules and interior areas