Thanks for posting the link to the image. For my taste it's a bit too simplistic but nonetheless contains some useful information.
I think the ordering of the steps is not correct - I would assume that these updates are integrated once they are ready. The time needed might vary considerably.
Libsecp256K1 got added in 0.12.0 as far as I remember, and it made bitcoin much faster to open since it doesnt take ages to validate transactions anymore, we go much faster.
Yes, libsec is already deployed. However, in my case I didn't notice a significant performance boost. Could be that my computer is too dated to profit from the optimizations or there's a different bottleneck. Nonetheless it was a great update because it reduced dependencies on external libraries and improved security.
I'm really looking forward to SegWit. I think a successful upgrade will end the exhausting blocksize debate forced on the community by some fanatics by proving that there is a much more intelligent way to scale Bitcoin.
ya.ya.yo!