Updated: Comment #0
adds the ability to import single config entities.
Once committed, it will require you to have the ID specified in the YAML you are importing, which is a reasonable expectation.
However, in D7 Views, it let you choose to rename it anyway, and we could possibly do that here too.
The biggest problem would be conveying that they shouldn't include the config prefix, but that could be solved by adding a field_prefix to FAPI on AJAX.
Add a textfield allowing a custom ID that would override any set in the YAML
Decide if it should be made required
User interface changes