I can't speak to B&N's offerings on technical subjects as I don't read them, but question for you - did you find the offerings in the Sony ebookstore limiting? If not, you can purchase new books from Sony and transfer them easily to the nook. to compare B&N to Amazon is kind of apples to oranges; however, if Sony's offerings met your needs, then by default the nook would be okay as Sony books can be read on the nook. As far as an official statement or announcement from B&N about future offerings in technical subjects (or any subject, for that matter), I haven't seen or heard anything.
As for your questions on viewing PDF files on the nook, there are several current discussion threads specifically on this topic. There's even one within 2 positions of this thread currently with PDF in the topic - it's probably helpful if you search the forums for prior discussions, as someone is unlikely to come to this particular thread and reiterate the same points.