Troy has been updating the roadmap a bit here:
https://github.com/troyjfarrell/tempest/blob/main/doc/roadmap.md but a lot of the core features should look fairly similar to Sandstorm, so if you have a good feel for what Sandstorm is and where Tempest is at, you might start to get an idea where you can build on. Since Tempest is still at a fairly early stage, there's probably a fair number of areas work needs to be done that isn't particularly difficult, but you will probably want to get familiar with how Ian laid out the project.