1. The metabones adapter has that tripod mount thing that makes it difficult to fit in a housing, unless housing manufacturers make an allowance for it.
2. Even if it goes down to f0.7, nobody is going to shoot at the f stop because of the hyperfocal (eg. 20mm) is about 20m? The metabones is great for terrestrial filmmakers, but the application won't solve the problems of noise, even on the S35 4k (if and when it comes out!)
1) Metabones converter for BMPCC makes your not so wide nikon slr lenses into allmost the same f.o.v as APSC lenses have and increases your light transmission by 1,67 stops. Problem solved I think, but also creates the need for a way to adjust the aperture ring on the Metabones speed booster.
2) The above takes care of some of the low light issues?
3) Easily taken care of by adding a little space inside the housing or if need be a external battery enclosure. If you don't go this route you still have replaceable batteries that last about 45 min. Not ideal, but doable.
…or am I missing something?