Gmail looks to be on the way out as Google's free email service, to be replaced by Inbox - which Google has been experimenting with for some time. Gmail is over 10 years old now, even though it spent a lot of that time in "beta".
As a Gmail user myself, I have not yet taken up the invite to try Inbox, but this Forbes article indicates that yes, the plan is to ultimately shift Gmail users to Inbox - and one assumes that existing emails and attachments will carry over, much like when Microsoft's Hotmail users were switched over to Outlook.com.
Forbes[Inbox] uses standard gmail accounts and Google played it safe by operating it as a standalone Gmail alternative. But the two were never going to be remain permanently separated. Google doesn’t create major services for them to remain niche. It has shown that with many ruthless culls in the past, including that of the beloved Google Reader in 2013.