Hi all, let me start that my goal here is NOT to start a polemic on the reasons for using nasal vs any other scripting language, or the scripting vs native code, or any such argument :)
Thanks for remembering that.
That said, being a long time user and proponent of levering scripting in games/sims, and particularly, using Lua, I have a keen interest in any insights garnered over time by current and past fgfs devs.
How coupled are Nasal and the scripting glue in FGFS ? Is there a clean break, or if not, can it be refactored without too much pain into something that would allow end dev users to use whatever scripting language they prefer, or have many modules already writen in, etc.

If the coupling is not of the hair pulling type, it might be conceivable to integrate another scripting language alongside Nasal for starters, and in time, completely replace it if one is so inclined :)

For me, this would be Lua, and I'll be working on integrating it in my local fork, but as I'm just getting down to tinker with FGFS source code, I'm interested in hearing your views on the topic. If there is interest in this beyond my own, I'd rather do it in a collaborative/friendly way that's not one sided, or in other words, I'd rather not rip out Nasal savagely to replace it completely with Lua, without thinking about compatibility down the road.
My preferred approach would be to start with cohabitation, rather than coupling Lua to a local fork...
What I'm interested in hearing is about the collective and individual experience of working with Nasal at the source code level, the API/communication mechanism between its VM/interpreter and "native" code, and plenty of other documentation details which do not seem to exist or that I haven't been able to find, and can save a lot of time in coming to grasp with code you haven't written.

Thanks in advance for sharing your experiences with Nasal integration,

Be Kind.
Remember, everyone is fighting a hard battle.