First of all: Thanks a lot for your awesome progress on this plugin today!
I've just tried it and it seems to work well on the root level. However, auto-completion doesn't seem to work on a sub-level. Here is an example:
# auto-complete works for `my_field`
my_root_field: 42
my_other_root_field:
some_dynamic_key: # this key can be chosen arbitrarily
sub_field: 0 # this again is a concrete, pre-defined key: auto-completion doesn't work
Out of curiosity is sub_field a child node of some_dynamic_key and some_dynamic_key a child node of my_other_root_field? If this is the case then it looks to be a bug. The autocompletion was built to be context dependent so as long as some_dynamic_key is a child of my_other_root_field then it should autocomplete with sub_field.
Heres a demo of how it should behave:

(I used http://json.schemastore.org/swagger-2.0 as my schema)
What you've posted seems to work for me but here is what doesn't work for me:
"yaml.schemas": {
"https://raw.githubusercontent.com/graphcool/graphcool-json-schema/master/src/schema.json": "graphcool.yml"
},

At the current time the auto completion is context dependent only. Since some_name isn't a child of functions we won't be able to autocomplete anything under some_name. Additionally, auto completion is provided for results that are valid according to the schema, since some_name isn't valid in the schema as far as I can see it wouldn't autocomplete on that either.
I'm not sure why you think it's not valid? As you can see here in the definition functions is of type: object which should allow for arbitrary keys. The values however are of type: #/definitions/function.
So either we've misunderstood JSON schema or this seems like something this plugin should support 馃檪
I'm working on adding this now. I think I was just confused as I haven't seen that before
It's awesome that you're working on this. Is there any rough eta?
It should be ready in the next few days!
@schickling We just updated the extension with a brand new autocompletor! It now fixes this issue and does autocompletion on values in the schema as well!