I've issued a PR for YTEP-0013, which tries to promote deposited particle fields to being a first-class field type. This extends the (field_type, field_name) syntax, adds a new concept of the 'deposit' field_type.

If you're at all interested in how particles are treated in yt, I'd encourage you to look at the PR and comment!

https://bitbucket.org/yt_analysis/ytep/pull-request/15/ytep-0013-first-class-deposited-particle/diff

Thanks!

chris