Persons really need to be indexed first.

Preferences were reindexed early, because they are needed
to index documents requiring access to a conversion server.
This must not be required to reindex users (which just happen
to be Person documents so far) as they are needed to index
security properly and categories.
Do a shallow reindexation of person module on first pass.

Person subobjects are not needed after first pass, so don't
waste time indexing them.