What "finished" means in this context is that we've established which problems we're going to solve, and the solutions to those are well-understood. There aren't new problems that node-core is setting out to address by making changes to the binary itself.

The new hard things to tackle are above the core layer - CI, userland module documentation and discoverability, binary deployments, etc. There's quite a bit of polish and refinement to be done at the lower level, but the paths are clear at this point, as far as that goes.