We should increase range of upgrades that can be conducted as a "soft" upgrade rather than a "hard" upgrade (requiring a blockchain restart). The related RFC, which is now open at tendermint/spec#222, has more detail on the proposed solution.

Combined with upgrade tooling (#5595), it will be much easier for users to upgrade Tendermint Core.

Version numbers will play a key role in this. Here are a few outstanding issues that deal with versioning across Tendermint Core:

• Add version to KMS handshake: KMS handshake with Version #2665
• Converge on AppVersion: Convergence off AppVersion #2448
• Version WAL: Improvements for WAL #785