I think what will make the most difference in the long term is using GNU Guile Scheme as language for package definitions. I think it is a brilliant choice to use a mature and popular language which supports functional programming very well. The fact that Scheme is minimalist and easy to learn will without doubt help attracting contributors in the future, and this in turn will be decisive for driving adoption in the long term.

Another feature that is very nice is that there is no difference between a package definition in a local development environment, and a definition in the official channel. What you put together as a build recipe of a tool that is useful for your quirky local project will also work as part of the distribution.