Here's a half-cooked idea which might interest some people. I tried to improve upon the design of Le Corbusier's Unité d'Habitation.
The original design (borrowed from Russian architects; see Frampton's Modern Architecture) was quite clever and remains a fascinating prototype. Practically every student of architecture studies it and designs a variant. The appeal of Le Corbusier's design is that it's very efficient but also very humane. Because of the sectional composition (see image below) each unit is allowed to have a "double orientation"---east and west in Le Corbusier's case---whereas a typical plan with a double-loaded central corridor gives units access to only one orientation. Le Corbusier's design also gave each unit a double-height living room. And because the central corridor is only needed on every 3rd floor, the building becomes quite efficient, although it is inefficient for each unit to have its own staircase within.
Le Corbusier oriented the Unité d'Habitations---all of them---to face east and west (as I explained in Le Corbusier and the Sun and Zeilenbau orientation and Heliotropic housing). This is somewhat problematic, as half the units have their double-height space dark in the mornings, the other half dark in the evenings. Nobody gets the excellent south exposure, and shading is very difficult on the east and west. For general energy efficiency, a long, narrow building ought to face south. If you simply rotated Le Corbusier's design 90 degrees, half the residents would have their living rooms facing north and be sequestered to a kind of 'thermal ghetto' (see Public Housing and the ‘Thermal Ghetto’).
So how could the Unité d'Habitation concept be refined, to be rotated 90 degrees, and give each unit access to the sun? Here's my rough idea. South is to the left.
This creates a 4-bedroom unit, and a 2-bedroom unit, each having a 1.5-height living space (LR) facing south. Of course it could also be imagined as two 3-bedroom units with three-dimensional interlocking. In any case, balconies and shading could be added. Kitchens and dining areas (K&D) are 'buried' in the center of the building, though I think these spaces would have a view of the sky through the living room. Winter sun can penetrate deep. Bedrooms face north. (The section has no depth, so the bedrooms indicated are two-deep.)
This scheme retains the value of a central corridor on every 3 floors. And, as in Le Corbusier's design, each unit has cross-ventilation. Emergency egress issues have not been resolved. Above, the sloped lines represent stairs; they could alternatively run perpendicular to the section view as shown here:
Worth developing? Comments welcome!
Edited to add: A friend suggested ascending from the living room to the bedrooms, rather than descending. Here's how that would look:
More variants based on feedback:
Edited to add: I've learned from the excellent Single Aspect Blog that this form is known in Europe as the "scissor maisonette" or "scissor block planning," and that the 'ascending' scheme above unknowingly recapitulated a 1960 Kenneth Frampton housing block in London, though Frampton's building was oriented facing east and west.