I am thinking Fortran but separate as a plugin. It looks so far like fpm build --dump is calling the printer and generating a file. There are TOML and JSON libraries available, and the TOML interface library is already an fpm dependency. So creating one plugin using that method provides a skeleton for others that have been discussed.
For starters I think I will try that approach and do something simple like set all the FPM environment based on the invocation and then start a subshell so all the defaults are set until the shell is exited. . Being in Fortan if it looks like the interface generator should become part of the monolithic core of fpm little effort is lost as all but the read of the dump should just be code that is moved to and called from fpm, but it frees up prototyping from needing to be synched with fpm itself.
One of the test programs (just looking at it now) looks like it might be doing something close enough to that to be reworked into a prototype for just loading the model from the -dump output.
But I also see the printer from fpm build --show-model. Not quite sure what the pros and cons of the two printers are a the moment but thinking the standard JSON/TOML files are preferred as they are using a standarized (well, pseudo-standardized) format (?)