You already could, before this announcement. For example, want to join https://gitter.im/hashicorp-consul/Lobby ? Then join #gitter_hashicorp-consul=2FLobby:matrix.org from Element.
You can also click little discover icon on Element and search Gitter for channels.
That being said the bridge is very flaky. Sometimes my messages would not get delivered and attachment such as schreenshots never work either. For the most part it's quite functional though!
yup, but the experience is pretty dire, particularly on the Gitter side of the bridge. The intention instead is to be able to join #hashicorp-consul_lobby:gitter.im in Matrix, and have all the Gitter users natively there in Matrix... but also all the Matrix users there natively in Gitter :)