[frank]

It's something I've been considering as well.

In fact, I created a table that compares lenses in terms of weight and volume, between MFT and Fuji.

 

Some lenses are a bit different (MFT 12 and Fuji 14), but this is more to get a rough estimate of whether one would gain much by going the MFT route. Furthermore, the speeds are also a bit different too.
 
I only included primes, from the widest available to the classic portrait focal length (~85mm equivalent).
 
Note that I included results for two 85mm equivalent focal lengths: one with the Olympus 45mm f1.8 and the other with the new Panasonic 42.5 f1.2 (numbered "MFT (2)").
 
As we can see there are significant gains both in term of size and weight by going the MFT route albeit with generally slower FF equivalent apertures. Also, the gain is much less if one choose the Panasonic instead of the Olympus, at the cost of speed/DOF of course. Also, overall the Fuji offers more speed and DOF control (obviously).
 
So, as with everything in life, it's all a matter of trade-offs.
 

 

Frankly the table does not convinve me. For example, Pana 14mm and Fuji 18mm are not directly competable. One is pancake with F2.5, the other is a regular lens with F2. The same goes for the Oly 17mm vs Fuji 23mm:  a f1.8 lens with decent IQ vs a f1.4 lens with super IQ. I also think the Oly 45mm should be compared to the Fuji 60mm: same equiv. FL, similar equiv F.