If it's possible to build things for the Decker ecosystem using Decker or Lil, it's advantageous; it will be easier to keep things up to date and portable as the platform evolves, and to reuse bits and pieces for other Decker-related projects.

That said, anyone interested in building tooling is welcome to do so. This is why, for example, the Decker file format is fully documented: https://beyondloom.com/decker/format.html