Looks promising, and support for huge files is a weak point in vim, so I gave it a try. My usual workflow with big logfiles is to zoom into certain types of messages with e.g. :v/error/d and back out with u, and alternatively jump from one occurrence of a string to the next with *. That doesn't seem to work, so for the moment it's not the right 80% for me. But I do think it's a worthy project, so I'll keep an eye on…
Navigating large files with motions like 50%, 70% should however be instantaneous. Navigating by line number is again somewhat slower, because the file actually needs to be read in this case.
Aside from that :v/ has a different meaning in vis.