Hello!
The first prototype of Gerbil integration inside plain Gambit is a reality: https://github.com/mighty-gerbils/gerbil-gambit
What this provides is Gerbil as Gambit modules, which can be used directly from vanilla gambit programs. Note that this is just the runtime part, but there is a wealth of libraries that you can benefit from even without the macros. Also note that this is the first prototype, so there could still be latent bugs; please open an issue in the repo if you run into trouble.
-- vyzo