What I want:
2-5 GA aircraft flying closed pattern touch and go/taxi back
Operations on parallel runways
Uncontrolled airfields with unicom chatter
Tower ATC at controlled fields
Offline functionally
It seems like almost all the existing AI Traffic add ons and utilities are focused on airlines. And the GA focused ones seem to just add arrival and departures, but not much interesting interaction.
Have I just missed this?
No you haven’t missed it. So far as I am aware it doesn’t exist as yet. All we have at the moment is the mod that allows the use of GA only from the Asobo default AI traffic which gives limited arrival and departure activity. All other AI traffic development work is aimed at airlines as you say.
Try PilotEdge.
Live pilots, live ATC, and they have “focus fields” daily where they encourage busy pattern work.
True…I’m a super fan of controlled network (thousands of hours as pilots and ATC) BUT we are also thousand flying in area where there no control when you have time to fly or not enough activity. I would love to fly in US (with my free scenery) but unfortunately my spare time (in France, Paris) doesn’t fit well the time coverage of PE 
I start seeing more traction and requests for a better support of GA (air club, 150/172, Piper…) by MSFS nor only take-off/landing but also pattern work. The trick (like this one How to get GA traffic when using AIG, ST, etc. - UPDATED) to mix with AIG/SP/FSLTL/FStraffic doesn’t create enough local traffic.
It sounds like you might want to organize a small group fly-in, using Discord (?) as a way to communicate with others in the pattern.
Like a Bush Pilots fly-in that you’d organize.
I’d check them out and perhaps ask the organizer how they set theirs up.
Would you mind letting me know a little more about this mod you mentioned? What is is called and can you point me towards where I can download it please?
There’s one here:
Thank you. Is this one that you have used? If so, would you recommend? Are there others on the market which do the same or even better? I am just trying to inject some GA traffic goodness into the sim, but without causing any detrimental side effects! Thanks all 
Yes I’ve been using it for over a year with no problems. There are a couple of freeware GA traffic mods on flightsim.to; GAMod and GA Stock Aircraft Traffic which you can try for free.
It exist some versions of GA Traffic programs, but nothing that really works well, my hope is for the FS Traffic GA update.
Try a PilotEdge subscription. Real controllers & actual pilots in the pattern. They have “focus airports” where they encourage simultaneous pattern work daily, which is to say NOTHING of their AWESOME CAT and IFR ratings.
Nothing beats it. PilotEdge.net