If its:

a) Reasonable,

b) transparent,

c) non-discriminatory of that traffic type,

d) there is temporary and exceptional network congestion,

e) measure is not be maintained longer than necessary.

If all those are true they may throttle torrents. A key word here is transparent, since few ISP even admit that they throttle traffic.

Well, based on that quote they can throttle what they want - but they have to do it equally across all similar applications. So for example they can't throttle Youtube and not throttle Netflix - they have to throttle both (or neither).

Well, that depends on your interpretation of "functionally equivalent". Is Youtube functionally equivalent with Netflix?

Spam-Emails, DDOS attacks and Http Traffic aren't functionally equivalent, which is probably the point.

I think the definition will also include the question of competition between the traffic streams. Youtube and Netflix are competitors, whereas an E-Mail Service and a Gaming Service isn't.

Net Neutrality should not mean we have to build the infrastructure that can faithfully execute DDOS attacks. Now, if we want to build the infrastructure to let all internet users stream 4K Video 24/7, is a whole other question...