My general thought is that we should formalize all fields that we expect/hope people will use when manipulating data.

So if you have a mostly read-only string field that just shows up in a UI (like a wordy description, or user-defined tags) then that would go in a general keyValue pair bucket.

If you have a field in which the format of that field is really important (because its an int, and you multiply it - or its a quality score and you sort by it), and, the community has decided that the field should be used in that manner (so not a crazy one-off field) then I would hope we make it first-class.

So if you wanted to do a full variant analysis, you shouldn't need to use the info tag at all. At least that's my goal :)