In April 2016, Microsoft's self-imposed goal for completing the migration of the vast majority of Outlook.com users to the new experience was end of summer/August 2016. That date came and went. Around that time, some users said they were seeing error messages that stated the new date for completion was "first half of 2017." Microsoft officials denied this was the case, but it would not provided an exact (or even approximate) new date.
The reason I asked Microsoft again for an update -- besides prodding from the unmigrated masses -- was a quiet update to the company's plans for the rollout of the Focused Inbox feature for Outlook. Focused Inbox is the replacement for Clutter and is meant to help users automatically sort their email.
This made me wonder if April 2017 was the new Microsoft deadline for migrating all Outlook.com users to the new Outlook.com. I asked that question specifically, but Microsoft officials declined to comment.
The old Outlook.com service was running on a legacy infrastructure. The new Outlook.com is using "the same building blocks as the rest of Office 365." The result will be that new features can more quickly and easily be introduced across all the various Outlook apps, Outlook on the Web (OWA), and Outlook.com, rather than building multiple times for multiple platforms, Microsoft officials have said.