As explained in the Q major upgrade spec [1] we aim to implement 'proper' mistral workflows with dedicated CLI (i.e. no longer "openstack overcloud deploy -e upgrade_env.yaml" for the major upgrade) and UI.
There is already some work underway for the mistral workflows and client:
https://review.openstack.org/#/c/463728/ Implement Upgrade workflow via the tripleo cli (python-tripleoclient)
https://review.openstack.org/#/c/463765/ Implement upgrade workflow in mistral (tripleo-common)
We can use this bug to track remaining work across the various repo (especially tripleo-common, python-tripleoclient and tripleo-ui which is new for Q). The proposed UI integration is a new feature and we'll need to discuss further and collaborate with the UI team.
[1] https://github.com/openstack/tripleo-specs/blob/master/specs/queens/tripleo_ansible_upgrades_workflow.rst
UI has been deprecated