First, I'm super appreciative of the work that's gone into improving Rigify for Blender 2.79! It's a great release, and a great new version of the addon. Definitely an improvement!
However, do I miss my old rig types. I have my own way of rigging things, and for me personally Rigify is now less useful. But I don't think this is actually a problem--rather it's an opportunity to do something I always intended to do with Rigify.
When I first designed Rigify, I didn't actually intend for it to only have a finite curated set of rig types (arms, legs, etc.). My intent was more for it to be an API and framework where anyone could create there own rig types, and mix-and-match as they pleased. After all, a production at studio A will probably have different requirements than a production at studio B. They should each be able to maintain their own rig types, metarig presets, etc..
In practice, I never got around to fulfilling this vision of Rigify--largely because it never came up. But I don't think it will actually be that much work. Rigify has, I think, a fairly stable rig type API now (unless I've missed something, I don't think it's changed in quite a lot of releases). Moreover, the rig types are already automatically registered simply by traversing a directory in the addon directory, so most of the relevant code already exists.
I would like to add a single field to Rigify's addon preferences that specifies a directory to look for custom rig types and metarigs. Any rig types or metarigs found there will then be registered along-side the built-in ones.
This will make Rigify much more flexible, without having to include every possible use-case in Rigify's default curated set of rig types. And for me in particular, it will let me get my rig types back without cluttering the defaults for everyone else.
Does this sound good? Are there any objections if I take a crack at this?