What is being removed is the replicator plugin (that used dsync).
That's what is being referred to in the video. Replicator hasn't been actively maintained for years now so this was dead code anyway.
Well, so Laura is absolutely right ...
"Things like dsync will be GONE in the community version."
That's not right, dsync is still there. Replicator is not, so dsync can't be triggered automatically by dovecot after changes to the mailbox (which is very handy for a simple "nearly live" Dovecot-aware backup mechanism when used on what is mostly treated as a single server setup, but with a replica on another machine).
There are other ways to run dsync, though not as convenient.
I'm still trying to decide how best to do this after replicator is gone. If the community version had obox (s3-compatible) storage I think I'd probably use that and e.g. replicated minio as backend, this seems like it would be more robust. As it is, I'll probably scan mailboxes for timestamp changes every few minutes and fire off dsync as needed.
Is s3 not to slow for this?