A lot of people has asked about a somewhat official roadmap/todo list for JSPrismarine. The following on top of already open issues is a basic gist of it and will be updated as we go along.
Anvil world support.
Multi-world support with dimensions (we should refactor/rework the WorldManager).
Crafting (shaped and shapeless recipes).
Chunk/Block-ticking (Grass-growing, ice smelting etc).
Add missing blocks & items.
RuntimeIDs.
NBT rework in style of GoMint.
Entities.
Survival mode (health, status effects etc for entities).
More involved testing (protocol, logic etc).
Get binary-release working on Windows and the newer macOS release.
Validate that the binary-release runs as part of GitHub workflow.