Since Beast supports fluidsynth instruments already, it'd be best to find out what the fluidsynth project needs for SFZ support and help them accomplish this.
Note that SFZ support could also replace the current bsewave file code by writing a simple Python script that extracts bsewave contents and generates an SFZ file.
Note that SFZ support could also majorly simplify imports of other multi sample formats, e.g. the bitwig multisample format is simply an XML file similar to an SFZ file for which a basic conversion could yet again be implemented via a simple script.
Many Soundfonts these days are provided as SFZ files instead of the SF2 format, example: http://virtualplaying.com/virtual-playing-orchestra/
Fluidsynth has already been extended to support SF3 (https://github.com/FluidSynth/fluidsynth/pull/354 - a Musescore extension to the SF2 files that supports vorbis compression, see https://github.com/musescore/sftools) and at least vaguely considered adding SFZ support: https://github.com/FluidSynth/fluidsynth/wiki/Future
Since Beast supports fluidsynth instruments already, it'd be best to find out what the fluidsynth project needs for SFZ support and help them accomplish this.
Note that SFZ support could also replace the current bsewave file code by writing a simple Python script that extracts bsewave contents and generates an SFZ file.
Note that SFZ support could also majorly simplify imports of other multi sample formats, e.g. the bitwig multisample format is simply an XML file similar to an SFZ file for which a basic conversion could yet again be implemented via a simple script.