I switched to 2.0-alpha and adding the following (usual) thing works !
<Hub Style="{StaticResource ActiviteHub}" caliburn:Message.Attach="[Event SectionHeaderClick] = [ShowDetails($eventArgs)]" >
...
</Hub>
And the usual x:Name <-> VM method binding works also for AppBarButton !<Page.BottomAppBar>
<CommandBar >
<CommandBar.PrimaryCommands>
<AppBarButton Label="Add a skill" Icon="Add" x:Name="NewSkill" />
</CommandBar.PrimaryCommands>
</CommandBar>
</Page.BottomAppBar>
Thanks a lot for your work and your help !