The closest examples of this (commercial/well-known) are the Orion and the R909, where the bass speakers basically only go up to about 100Hz, or 2-2.5 octaves. This is NOT a three way design, I can tell you that. And I don't consider design like this a three way either

I will be documenting the build with some detail.
As for inspiration, I have yet to research it throughly, once I see something I like, I'll be sure to post it. As of now I have not yet decided if I'm going to go it alone or derive off someone else's work. I may also totally make this a junk box project. It is a regular habit of mine, so don't hold out hope that my work is something you'll be able to work on because everything will come out of my junk box and locally available bits. And then it'll become both unique and useless for anyone else, an unfortunate combination. I'll try and make it duplicable to some extent though, and may serve as a starting point.
As it is my first priority will be the L18 and stands, the stands having monster subs built it. That is going to take quite a while, maybe four months or so, so don't expect anything before that.
What I have in the junk box are a pair of Philips AD163 tweeters and 4 12" drivers which need new cones, surrounds and voice coils. The bigger drivers will probably do bass duty, they were made locally to my specs about seven years ago and need to be rejuvenated after five years in cold storage. I have yet to crack them out of the wrapping. They are not subwoofer drivers, and not pro drivers either. They were specifically made for a low Q ported box application, so it's probably going to fit right in. We'll see. The tweeters are stock AD0163, and they work very well when crossed over very high (>4KHz).
The wideband will probably be the Alpair from Markaudio, Visaton T100 or similar, about $100 per driver. Research is still to throw up the right candidate, but I'd be looking at a low distortion unit with reasonable efficiency (I don't need >88dB), so the traditional widebands will probably get passed over (Fostex et al) for this project.