Are there two S-64 now?
Yes, fgaddon would be considered the FG supported version because it is fgaddon. My personal development repository will contain a variation. If I or someone else gets around to making a JSBSim FDM then there might be two in fgaddon.
I'm a bit concerned about that when and if the time comes because historically I have seen the JSBSim version eliminate the YASim version. It happened to me with the Cub. Once we got the JSBSim version dialed in, the consensus was to eliminate the YASim version out of fgaddon. I was a bit more green at the time and listened to others who I felt new best and it was removed. I was reluctant because I was very sensitive to the original authors. I don't think there was ever any blow back, so I guess it was OK.
What are the differences?
The irreconcilable differences are multiple derived effects, lighting positions, strengths and techniques, compatible modeling tools and to some extent organizational issues.
What's the plans?
Just as we have stated, Helijah will continue to use what he can periodically for the fgaddon version. The fgaddon version will lag behind my development version (would no mater whether we agree to everything or not). My development version will likely diverge in organization and the above mentioned disciplines.
Is it just the Compositor changes and the searchlight? I take the "stock" one won't get it.
No, actually that should get into the fgaddon version, if not already, in one form or another. Helijah is updating all his aircraft to use compositor lighting.
So if on Next it has to be wlbraggs?
No, you only need my development version if you want the most current stuff and the aforementioned differences.
Again, I emphasize, I really want to squash any negative discussion about right, wrong or best practices as I don't see there really is that concept in a completely open source project that can be so subjective. There is what is acceptable to the core and thus can be contributed to fgaddon, in this context I suppose both versions would be. Beyond that, I feel that is what personal repositories and hangers are for. You can disagree and still do your own thing. I think this is a strength of FlightGear not a weakness.