It would be a better end user experience if end users were able to navigate in the Knowledge Tier without having to leave the Stewardship Tier.
The plan is certainly for the 2 tiers to come closer together to provide a unified experience to the end user, whether that results in the embedding of the SKT into an iFrame or similar within the Stewardship Tier is to be decided. No current plans exist for this embedding in the current release plan / road map. If anything the ST would get embedded from the KT.
There will be 1 userID and they are different tiers of the same product. There likely won't be a need to embed as navigating between the two will become more seamless