Upload & Sell: Off
Possibly Metabones believes that a universal SB wouldn't be boosting their total sales. Better to have a number of customers buying two or three different SB versions that only one unit plus two or three different adapter mounts ?.
It could be also that a universal model isn't that easy to make. The front element of the SB is quite exposed even on a relatively thick version as the Canon EOS, let alone the Alpa.
See on the picture below how the front lens of the SB is almost flush with the bayonet. A universal model implies recessing some millimeters the flange to allow some space for the lens mount to fit. When swapping mounts, the sides and front of that lens would be on first line of fire, so to speak.. or maybe I'm totally wrong and we'll see the 'Universal' in a couple of months
On a different matter, the rear cap supplied by Metabones with the NEX versions of the SB is awful. Absolutely loose, falling from it's place just blowing on it. I have some cheap NEX rear caps that are also terrible in this aspect The original Sony is much better.
Luckily, messing with some spare caps, I discovered that Nikon rear caps fit very well on the NEX bayonet ( but rotating anticlockwise, of course )