I think that an important change that merits an edition is fixing up ranges, which became a RFC, was accepted and is partially implemented in nightly right now. If the work is completed in time, it should probably be included in Rust 2027.
Other things that might be included in Rust 2027 (or a later edition) are collected in the A-maybe-future-edition issue tag. While realistically perhaps not all of those will become a thing, I think that there's plenty of in-flight things that might be ready in time for a Rust 2027 edition.