Roadmap

What comes after the current release. Nothing here has a date.

Shipped

VS Code extension. Compares two huge files from VS Code and opens each difference in VS Code's own diff editor. See the VS Code guide.
rift serve. Rift's protocol for editors: JSON-RPC 2.0 on standard input and output, with a size bound on every answer. The extension runs it; Clients and protocol explains how it works.
rift git-diff. Git's external diff for files git calls binary, with Git LFS pointers resolved. See the git guide.

Directory diff. rift A/ B/ walks both trees in sorted order in bounded memory and diffs each pair of files under the same --mem, with a summary of added, removed and changed files.
Field-level key diff. Planned for 0.4. In key mode, name the fields that changed for a changed key: CSV columns, top-level NDJSON keys, COPY columns. Until then, --show-records prints both records of a changed key in full.
Exact diff for regions that share only repeated lines. Today Rift can replace such a region whole and marks it approx; an alignment that counts only the line pairs that match would make it exact.
Homebrew tap. brew install from a tap repository, added to the release installers once the tap and its token exist.

The limits Rift has today are on the landing page and in the README, under "What is not guaranteed".