The Objective
...to build a hybrid...an all-acoustic high induced-arch Tailpiece/Floating bridge guitar that combines the characteristics of an all-acoustic Tailpiece/Floating bridge Archtop guitar (example...1930's Epiphone Olympic   David Rawlins demo)
with...
a good Dreadnaught flattop.

1. I would describe it as an instrument that will have strong mid-range and clear piano-like bass notes and can deliver note runs without overtone blurriness.  This instrument delivers single notes, intervals and chords with great clarity uncloaked by accompanying overtones. 

Design challenge...The versatility of such instruments has been limited by the "clanginess" inherent in any Tailpiece/floating bridge guitar.

2. This hybrid must also be able to deliver just enough of the right overtones to mitigate the clanginess, making the instrument versatile enough for fuller chords and use in self-accompaniment.

 All things to all men?
...not possible.  In my mind I see a hirearchy of benefit, so from greatest to least benefit, here is how I see it:

Crosspickers
I'm confident these folks will love being able to play the crisp note runs and passing notes in and out of chords.  Particularly good for the self-accompanying solo performer and great for self-accompanying solo of up-tempo songs.
Swing / Gypsy Jazz Players
This design is a direct off-shoot of the Selmer-Macaferis that Django played.  Django played the lead with the Small mouth Selmer, brother Joseph played rhythm with the Big Mouth.  The Gypsy hybrid should do both.
Lead guitar players
This is an acoustic that will be effective in accompanying a rhythm player/front person.
Fingerstyle players
Folks from either the Flattop or Archtop world will enjoy the hybrids.  Archtop folks will feel a familiarity with the crisp notes and Flattop folks will appreciate the enhanced projection.
Finger pickers
The enhanced single note clarity and additional volume will take some getting used to.

The challenge...
Your flattop guitar benefits from its wash of overtones, which cloaks imperfections in intonation and tuning. A Gypsy hybrid is not forgiving. Intonation and tuning must be precise. These guitars are not for beginners.

 Physical design...delivering energy to the soundboard
A Tailpiece/floating bridge hybrid guitar creates sound in a much different way than a Flattop/push-pin guitar. 

Tailpiece/floating bridge hybrid guitar
The strings push down on a one-piece ebony bridge so the soundboard is excited in a predominantly up & down motion.  The tension of the strings is distributed in a loop, actually a pyramid shape.  From headstock to bridge, to tailpiece and the return is up the back of the guitar to the neck. 
Flattop/push-pin guitar
When a string is plucked, it is pulling up on the top and at the same time jerking it sideways.  For a Flattop, the energy of the string must pass through the saddle, the bridge and down into the body secured by a push pin.  If you count it all up, that is eight components affecting the soundboard. 

It seems impossible not to conclude that the Flattop gets the lion's share of it's wash of overtones from the way the strings join the soundboard and likewise, the Tailpiece/floating bridge guitar gets its strong projection and lack of overtones from the way it delivers excitement from its floating bridge.  I have noted that if two acoustic guitars have the same body shape and one is Flattop and the other is Tailpiece/floating bridge, the Tailpiece guitar will deliver significantly more volume.  Conclusion... the tailpiece guitar is more efficient in terms of converting kinetic energy into sound.  Finding "good" overtones has been the essence of this project! 

 Physical design...The soundboard
The soundboards of both types of guitars start with the same thin (2.5-2.8 mm) wood.  I started with Cedar but gave it up after 9 prototypes.  Cedar makes the "clanginess" problem much worse.  Spruce is best! 

Tailpiece/floating bridge hybrid guitar
The soundboard is forced into a high induced dome (16' radius) with profiled radial bracing.  The principle bracing is the "X" that transfers the energy of the bridge to the soundboard and prevents the downforce of the bridge from rupturing the edges of the soundboard which was happening to the first 4 prototypes.  The "X" is not jointed at its crossing.  Tone seemed to improve when I stopped lap jointing the "X" at the crossing.
Design Challenge...reduce bracing and improve soundboard response.  Reduce it too much and the bracing at some point will lose its ability to hold the high dome.

Flattop/push-pin guitar
The soundboard is forced into a shallow arch (30' radius is typical) with profiled bracing.  Martin favors the "X" that is lap-jointed at the crossing.  Taylor now uses "V" bracing.  For Flattops, the bracing resists the tendency of the strings to pull the soundbard up and in the direction of the headstock.

 Physical design...The back
The back of the Gypsy hybrid is the same as most flattops.  The hybrid is forced into a 16' arch with the ladder braces profiled accordingly.

 Physical design...The neck
Obviously, neck profile depends on personal preference.
 
 "Zero fret"
What is different with the Gypsy hybrids is the use of "Zero fret".  Macaferi used it on the Selmers and Chet Atkins got Gretsch to build some guitars this way.  Instead of a nut there is a slotted guide above a new first fret which is called the "Zero" fret.  This makes it unnecessary to deal with intonation at this end of the guitar.  With most guitars, playing with a capo makes holding down strings easier since a nut typically has the strings up a bit higher.  With "Zero" fret, you get the same feel wherever you play.  One drawback that has been noted by others is a high wear rate on the "Zero" fret.  The remedy has been to use harder stainless steel for that fret.  I've been using "Zero" fret since LG-9 and haven't seen any downside so far.
Take a look..."Zero" fret minus the string guide.

Bolt-on neck
This system works well combined with mortise/tenon joint.  The body and neck can easily be separated since the fingerboard floats.  This is of great benefit in simplicity of construction and finishing. Expensive neck resets would be a thing of the past.  Taylor, Collings and others have gone to bolt-on necks but the fingerboards are still stuck to the guitar.
Take a look at bolt-on neck