I'd propose that:

• Foreman 1.6 has API v2 as a stable, supported API on par with API v1
• Foreman 1.6 continues to have API v1 as the default (i.e. when no accept header or versioned URL is used)
• 1.6 release notes strongly recommend users switch to versioned access (at least) and to begin migration to API v2
• Foreman 1.7 makes API v2 the default, v1 becomes deprecated (possibly via a plugin which may not be installed by default, if we feel that's easier to maintain)
• Foreman 1.8 either won't ship v1 or it may be available as a plugin

So this ticket should remove the experimental label from v2 and call it stable in the API docs.