It's always hard to comment on these things with a limited knowledge base, but he's a try anyway.
Inboard rears, easier to justify because you already have a drive shaft - but presumably the torque created by the
brakes is much greater than from acceleration, so this item would need to be stronger/heavier than it is (not forgetting the reversed loads already discussed - just twist a pencil between your fingers to re-assure yourself which way they work
).
Inboard rear
brakes would surely interfere with the size/shape of the diffuser (maybe that's why they moved outboard again in the 1980's?).
Inboard fronts - you are adding an extra component (again would need to be very strong as the fronts still do most work). Then you would need to house and cool the
brakes in the nose, making the nose wider. As far as I understand the air-flow between the wheel and the nose is critical to the performance of the rear of the car, so you probably compromise this for a small improvement in un-sprung weight. By adding a front driveshaft, you had a little to rotating masses (more spinning stuff to stop).
What will all that heat do to stuff in the cramped nose area - dampers/hydraulic fluid/power steering (driver's feet).
All in all, with race tracks being much smoother than in the 1960's and carbon
brakes being very light, easy to cool (and compact enough to tuck into a wheel) the added complication and compromise elsewhere will be less than the gains from reducing unsprung weight.
A little add-on thought - I expect getting rid of heat from the outboard wheels is much easier than from the nose area and adding another heat source around the engine/gearbox cannot be a great idea.
Final one -
- I understand that the heat from the
brakes is pretty handy for heating tyres.
)