From what I've read and understand I see the following:
SPF is something which can be setup by the sender (on the domain level). Say you are the owner of example.com, you could setup an SPF record to allow only emails from example.com and localhost/127.0.0.1/your ip address) to be sent out through the server.
DKIM almost sounds like a chain of custody and makes me think of CSI
(Read about DKIM @
DomainKeys Identified Mail (DKIM))
The whole idea of DMARC from a phishing standpoint (which is what it seems to be aimed at) sounds nice, on paper. Just thinking out loud here, but what if somehow someone at the powers that be decide to "block" your domain from sending or receiving. If they can somehow set your domain as "untrusted", you could be screwed.