The features of the Hub are not gone in most cases. The concept is. Easier to understand once you’re using it. Just forget the Hub concept and think of it fresh when you see it. You can still designate local network API access.
V6 and V5 do not interact whatsoever. You can run them alongside each other. V6 performs a one-time configuration upgrade on the local device without touching your V5 config and from then on the apps have no relation to each other.
One feature we did remove in V6 is Remote Access. This feature never belonged in the product. It was convenient to access your home network devices without a VPN, but required a large array of functionality on our side that made the product far more complex when the problem is much better solved via 3rd party VPN software. We recommend OpenVPN, but of course there are countless VPN solutions, and using such a dedicated solution for the small number of users that required this is far superior. From a security perspective, it is also desirable to have fewer things opening ports on your router. A VPN is the correct solution to this problem these days, so this feature was removed.
Other than that, the features that were provided by Simple Hub will still be provided by some device on your network.