We're glad you're as excited as us!
It really is very early days with the vidding archive, so we haven't made any definitive decisions. Vids require quite a substantially different framework from fic and archive, and there are also different legal issues, which is why it's scheduled as a future project rather than rolled into the main Archive. It is likely that we will have some connection between the Archive of Our Own and any vid archive we build - whether just a shared look or a completely connected interface - but what goes on in the backend of the code may have to be quite different.
As this is still in the early scoping out phases, we're not set on any particular technological solution yet - we're exploring the options. However, we're excited about some of the things emerging at present, such as bittorent/streaming technology. This kind of stuff is quite complex and specialist, which is why we're not looking to build it completely from scratch - when there are great solutions available to coopt, we want to use them! (In a way this is what we have done with the existing Archive, since we use Ruby on Rails, which is basically a big library of awesome code which we can draw from.)
Thanks for your questions! We'll keep updating as we have more to tell on all these issues.