ok, regarding the testing then.
does it affect only ship tree classified boats or all of them?
for example, you can test skeleton sub BO's turn rate on premium and event ships too, since you probably have a not trimmed/skeleton BB or CV BO.
but if it's tied to a ship tree, it'll be hard to test, since you gonna need 2nd sub BO, fully crewed.
Now regarding skeleton sub BO, it's worth doing that:
for speed (the reduced weight),
ability to drive lower tier subs,
more bulge/belt armour.
The only usefull feature right now which you loose by skeletonizing sub BO is, torpedo spotting range.
And the additional repair and soft defence stat provided by BO, which is very small.
I would rather fit in another repairer, because of skeleton BO and trimmed to 1.06mil true ability torpers (saved weight remember?).
Where's richardphat, a good tester when you need one? ;)