I've not seen the FS mp3 module - but I agree in principle with rl. If I want to play mp3 recordings, I've got a lovely little iPod (or RealPlayer on my PC).
I guess it's not included in SM because even the dev's have realised that it's not a lot of use to plugin builders.
Surely, at the very least, mp3->mem wouldn't be so hard to do, that would go a long way to being useful (mp3 format for samplers etc.)
Given that SM is supposed to be audio DSP specialist software, surely load/save/HDD-streaming of any available codec wouldn't be unreasonable - I know some encoding algorthms are "intellectual property" but I don't recall not being able to access a codec purely for playback at least.
Feel free to use any schematics and algorithms I post on the forum in your own designs - a credit is appreciated (but not a requirement).
Don't stagnate, mutate to create. Without randomness and serendipity the earth would be just another barren rock.