To some degree, but Echo is not set up for long messages. I can see a Flow+Echo newsletter working something like "create a newsletter thread on [project] talkpage, tag all newsletter recipients, it'll show in their boards and also on the talkpage for people who drop in, and they'd be notified of it via Echo".
Echo is totally (potentially) good for things like "hey! there's [[a thread you should participate in]]", or will be once other features are built and SUL finalisation is complete - but they've not be, it's not, and a newsletter is a very different beastie.