No-one knows. When Gutenberg is ready. Are some common answers. And I don't know anything else.  The official WordPress 5.0 release page has not been updated since November 2017 and features lot of "TBD"s.  We need to wait for a public discussion of the merge proposal once that's accepted, a Kick-off Meeting will be scheduled. I estimate that we will see a 5.0 Beta 1 version Mid November just in time for WordCamp US. Matt Mullenweg, co-founder of WordPress and CEO at Automattic, might include lessons from the merge proposal in his annual "State of the Word" (STOW) presentation. After that we might see a 5.0 Beta 2 Mid December just before the holidays.  Everyone will be out until Mid January. We start again with Beta 3 and Beta 4 . The RC 1 might arrive at the end of February 2019 with a final release in March 2019. For our company planning we will wait with upgrades and training of content creators until 5.0.2 or 5.0.3 are out. Planning-wise that brings us to Summer 2019. I might be totally wrong. I have no particular insight into the planning. I follow #core and #core-editor meetings on Slack, read GitHub issues and check on the progress of milestones.