It would be good if there was a way to delete projects, in addition to archiving. Currently, I archive projects and decrease their visibility to achieve a pseudo-deleted state.
In many cases, however, I wish to merge a project into another project (duplicates) or even forcibly delete a project (people seem to create usepess projects at times).
We plan to provide a more general/powerful bin/project destroy at some point, which will be able to destroy projects. However, Phabricator is built around making actions auditable, so the expectation is that object destruction is a rare event which may reasonably leave rough edges in the application. We are unlikely to ever change this or make object destruction easy/common/clean. It runs counter to product goals (actions should be auditable; users should be accountable for their actions) and is technically difficult in some cases (objects can be associated with millions of other objects, so object deletion can take an arbitrarily long time -- fine from the CLI, but problematic from the web UI).