I'd like to see something like the Allis Chalmers G or Hefty G but a more modern version of it like they have in Europe which they call Tool Carriers.
On both the Mazzotti and Tracmaster, you can adjust the length of the tractor via the center bar that goes to the front axle. Of course, you are limited to a certain length. They both appear to have hydraulic 3 point on the rear and mid-mount. One of them appears to also have a PTO at mid-mount as well in the rear.
A lot of these appear to be used in pine tree nurseryes. I know of place in Canada that sells the Egedal Tracmaster. However, it is very cost prohibitive at $100k for the 2WD version (400) plus shipping from Denmark.
I've been looking at hydraulic motors, stearable motors, pumps and systems to power a tractor like this. I also like the idea of having a hydraulic 3 point in mid and rear. If one used a a parallelogram setup cultivator like a Steketee Hoeing Element you wouldn't necessarily need a depth control (draft control?).
Once setup, I'd like to use is a front mounted side dresser or compost tea sprayer, mid mount cultivator and rear mounted sweeps to loosen the tire tracks. I'd also like to be able to possible remove the diesel engine for electric/battery power.
The one issue I see is switching out mid-mount implements. My easiest solution is to utilize an implement caddy but would probably require you to be on a concrete surface to easily move the caddies around.
The creeper gear would be nice as well to pull a transplanter reducing the need for an additional tractor for smaller farms.
Update: A French company Terrateck has created something similar to this. It's called the Culti'track. It's maybe a bit more paired down version than those I listed above. http://www.terrateck.com/en/portes-outils/50-tracteur-porte-outils-maraicher-culti-track.html