99.9% of people adopting the new version are not going to know what is in that new library or how it operates.
I lack the technical knowledge to give you an answer to all your other questions, but this sentence caught my attention.
I just would like to say this:
99,9% of the people already have to believe every other piece of code of bitcoin because they (me too) lack the skills to review it themselves.
This, in my opinion, is one of the biggest hurdles for bitcoin technology to overcome.