Moving user data from D7 to D8 Opigno Version

Hi, we are currently using Opigno for a multi client infrastructure and - by the way - liking the news about the upcoming Drupal 8 release! The new version, of course, seems to be very attractive, but we are uncertain about the upgrading costs considering user data transfer. Will it possible to move user data from D7 to D8 losslessly (the users including their content and activity tracking data) or are there foreseeable limitations? Any information would be helpful for us to develop an upgrading strategy. Thanks in advance! Best regards, Paul.