It is still in early access in Sencha maker of Ext.NET's underlying framework Ext JS; so work in progress. We don't have their deadline, so all we can do is keep in sync with them and try to release as soon as they deem Ext JS 7 released as well.
What we currently have from public news of the underlying framework: Ext JS 7.0 Early Access blog post
I don't see any firm date there, there seems still to have a substantial amount of changes and tests to do before release, and we must follow.
The only thing we could make right now about this is, re-establish single developer (or per-developer) licensing, even for Ext.NET 4 -- extending the license to Ext.NET 5 when it is released.
So, if you're holding yourself back because of multiple license acquisitions, you may find it worth going ahead and buying the 4.x licenses at once and getting started, as the upgrade to 5.x will be granted.
Hope this helps!