This is a proposal to add a Bridge Hub (BH) parachain to Kusama. All technical details can be found in the Bridge Hub Genesis release. The runtime is taken from the v9360 parachains release.
The BH will be the gateway between Kusama and other networks, like Polkadot and Ethereum. For now, the BH only contains some basic logic, and none of the bridge-specific pallets. Those will get added in future runtime upgrades; the goal of this proposal is to get approval from Kusama stakeholders and a "shell" operational such that bridge teams can focus on releasing their bridge logic, not launching a parachain.
The BH will primarily act as a message routing system within the network and between others. For example, parachains can configure their XCMP routing to interpret parents: 2 (indicating, "go to another consensus system") as something to send to the BH to handle. Likewise, the BH can handle incoming messages and route them to the correct parachain within Kusama.
Once operational, a Polkadot<>Kusama bridge will allow more interaction between the networks. For example, the Technical Fellowship can move onto the Polkadot Collectives parachain and serve both networks; or the Kusama network (as a unit body) could join the Polkadot Alliance.