The current plans are to provide version OMOP CDM v6 in ATLAS v3. The ATLAS (@Patrick_Ryan as a product owner) team is currently working on ATLAS 2.8 which - at least theoretically - should be the last major release in version 2. The team is planning to start ATLAS 3.0 work sometime in early Q2, 2020 but it will take a few months for the release to happen
So, my personal view is that if you do need a mature working environment across all methods and tools - you better stick with CDM v5.3.1. That was my guidence to our commercial customers as well.
Btw, are there any specific use cases you are targetting that warrant CDM v6?
Also, I think what you are highlighting is a current gap that I have been also advocated to fix for a while - it is to have a single OHDSI roadmap across all key components - CDM, vocabs, methods and tools (ATLAS, ACHILLES). We have attempted something like this last year. But it ended up being not that simple since OHDSI is not an organization - it is an open science community that lives on contributions and funding of its community members and thus it is a bit difficult to commit to specific timelines. However, I think we should still revisit the idea of having a single integrated roadmap, even if it is more of a vision