As Microsoft promised at Ignite (OneDrive Announcements at Ignite 2017) the Self Service Migration Tool kit has now been released.
The tool is supposed to help customer's migrate fileshares (SMB2 and later) and/or from other cloud services with the tool. As of now the tool is not available to be downloaded.
The official roadmap update is:
We are releasing our migration toolkit for self service users looking to migrate from share drives or several cloud based services to OneDrive on their own
Source: The Roadmap, item 23756
I will make sure to update this post or make a link to a new one as soon as I've tested the new OneDrive for Business Self Service Migration Tool kit myself.
It seems to be internal the Self Service Migration Tool that is used by FastTrack. Here is a short channel 9 movie about the tool. I will make sure to make a new post as soon as I've had a chance to actually test the tool.