It was an interesting and useful experiment, but unfortunately Google confirmed a few months ago that they would be shutting it down. The deadline was set for March 2019 and now according to a report from Ausdroid, it appears that Inbox users are now being greeted by a popup notification informing them that they should probably start making the switch.
For those hesitant to move back to Gmail, it should be noted that Google has since rolled out an updated UI to the platform where it is now considerably cleaner than before, so maybe it’s time to give it a try. For those who are worried about losing certain Inbox features, Google has published a support page where they share tips on how to get similar features of Inbox in Gmail.
They have also pointed out how certain features, such as Snooze, Follow-ups, Hover actions, and Smart Replies have also made it to Gmail. Admittedly the bundling feature was one of Inbox’s better features, and Google has provided users with some help on how to create filters and custom labels for your emails that should achieve a similar effect.