Let’s see:
multi-package project support (build all packages in one go, test all packages in one go…)
depend on experimental and unpublished packages directly, stored in Git repositories, not just Hackage and the local filesystem,
transparently install the correct version of GHC automatically so that you don’t have to (and multiple concurrently installed GHC versions work just fine)
We rely on ghcup to do this
optionally use Docker for bullet-proof isolation of all system resources and deploying full, self-contained Haskell components as microservices.
Automagic builds in docker containers are nice, perhaps not critical for adoption.