This story still enforce strict separation between Scrum and Kanban trackers. To make it short:

• None of the trackers used in Scrum can be used in Kanban
• None of the trackers used in Kanban can be used in Scrum

So it implies:

• Project admin can use a tracker in a hierarchy for Kanban as long as neither this tracker nor its hierarchy (parent or children) are used in scrum (either as backlog or planning).
• As soon as a tracker is selected for Kanban, either this tracker nor its hierarchy (parent or children) can be used in Scrum
• This consistency is ensured on Tracker hierarchy update/remove/addition

Examples:

Given the following hierarchy and Scrum configuration:

.
|--Epic
|  `-- User story
|-- Release
    `-- Sprint
Scrum Planning: Epic -> Release

-> No tracker can be selected for kanban

When I add "KEpic" and "KStory" trackers with hierarchy:

.
|--Epic
|  `-- User story
|-- Release
|   `-- Sprint
`-- KEpic
    `-- KStory
Scrum Planning: Epic -> Release

-> I can create 1 Kanban for KStory

Then:
-> Neither KStory not KEpic can be selected in Scrum part (planning or backlog)
-> When KStory kanban is created, I can also create KEpic kanban.

When I add "Task", under User story:

.
|--Epic
|  `-- User story
|      `-- Task
|-- Release
|   `-- Sprint
`-- KEpic
    `-- KStory
Scrum Planning: Epic -> Release
Kanban: KStory

Task cannot be selected for Kanban

When I remove hierarchy between KEpic and KStory:

.
|--Epic
|  `-- User story
|      `-- Task
|-- Release
|   `-- Sprint
|-- KEpic
`-- KStory
Scrum Planning: Epic -> Release
Kanban: KStory

Then I can:
-> I cannot put KStory in Scrum hierarchy (neither Epic no Release one)
-> But I can do it with KEpic (for instance if I rename it Bug)

+ Fix bug when no tracker available to create a Kanban