I definitely agree that the current implementation of having a free text field there is not good. A little over a year ago I discussed a plugin idea with a representative from Orcid that I met in a seminar. I was thinking that after filling an orcid id, you could "validate" it by checking what kind of info the API returns for that id by clicking a simple button next to the field. Basically to check if the returned name,email etc. matched. However, the representative, at least then, found that all forms of filling an Orcid that differ from their instructions are potential problems regardless of this kind of validation. I think that is the first time I heard about the idea of collecting them with an email + autehentication form.
I personally think that your implementation is much better than having just the open field and will definitely result into more filled Orcid fields. But the main risks there are the very same situations that Orcid was designed to solve, that is the authors with similar names, and the ease of filling the field with a search could perhaps lower the possibility of these kinds of mistakes happening? Fetching more user details from the account would probably solve this to some extent, but with the free API you are limited to the info that the users has made public. Even the name and email could be hidden from the free API. And probably, if asked from Orcid, they would insist on using their integration methods. But I am no Orcid representative, so I could be on the wrong tracks here.
Anyway, now I am going to stop whining about Orcid integration instructions
Again, excellent job on extending the plugin! Hopefully you will stick around and develop other stuff as well