Add an aggregator parser/processor for HAL

That's the "deserializer" that we've been talking about in various places. The caveat is that the REST approach is more of a push model, where you'd message a site and say "here, have this node" rather than aggregator's pull-based model.

I don't know what it would take to make aggregator parse arbitrary feeds, or in this case to route a specific feed to the existing Serializer/Deserializer support. Aggregator already needs love to eliminate Drupal 3-era code: #1839468: [Followup] Replace aggregator rss parsing with Zend Feed

If someone is interested in working on this I can certainly try to point them in the right direction, although I think Lin Clark would be an even better resource.

Aggregator isn't that bad anymore, and we're working on making it better, see for example #1930274: Convert aggregator processors and parsers to plugins.

Zend Feed is a nice idea but not an option until the zend framework guys fix their dependencies (and possibly composer guys their dependency management) so that depending on zend feed doesn't include the complete zend framework, see the issue for details ;)

Moving to 8.1.x

This would require setting up a matching entity type (with a matching data model). Feeds have a very limited, predefined set of fields. That's a *huge* difference.