See also: https://mtlynch.io/why-i-quit-google/
I hope with all the Inbox users/developers likely going back to gmail now, it will transition into the Inbox we all know and love.
Gmail categories are not the same thing as bundles. I love how Inbox condenses multiple emails in a single line showing you who the senders are. I think it makes more sense to show the senders before showing the subject of emails, and it's allowed for me to more easily digest the large number of emails I receive daily.
It's a shame really - IMO it would have made sense to keep developing the inbox concept, it is a quite different way of thinking about email, and if it's a separate app it can move faster than something which has to take into account all the legacy of Gmail. Far from the first time a solid Google product dies just because the dev team moves on to other things and nobody's working on it anymore.