Those slides are from 2017. P2P Matrix was released in June 2020. A lot of work is being done on Dendrite, the latest commit was posted two hours ago as of this

Those slides are from 2017. P2P Matrix was released in June 2020. A lot of work is being done on Dendrite, the latest commit was posted two hours ago as of this writing. From the GitHub page for Dendrite: "As of November 2020 we're at around 58% CS API coverage and 83% Federation coverage, though check CI for the latest numbers." So, yes, for now the metadata leakage is a real issue. However this is likely to change in the near future.