Google’s John Mueller posted on Twitter asking about webmasters who have done medium to large web site migrations recently, about their experience. He asked “how did they go?” Adding later “are the fears well-founded, if you plan & follow-through systematically?”
If you migrate your large to medium site domain name to a new domain name, did it go smoothly and as expected or did you run into challenges that were unexpected?
I guess this is Google trying to learn about how webmasters fear making such migrations and trust me, most SEOs do fear such changes. Google may be working on some new tools for site migrations in the new Google Search Console? Or maybe not, that is just my guess here.
Here is John’s tweet:

Every now and then I hear from medium-large sites that want to change domains and fear a loss in traffic. If you’ve worked with domain-changes recently, how did they go? Are the fears well-founded, if you plan & follow-through systematically?
— John ☆.o(≧▽≦)o.☆ (@JohnMu) July 8, 2018
Make sure to give John Mueller your feedback, you never know if that will make a difference to how Google communicates about this stuff in Google Search Console or what new reporting or tools they add because of your comments.
Forum discussion at Twitter.