Telegram would be an odd choice for privacy. Group chats are not end-to-end encrypted. Element would be a better choice, it allows to automate chat flows as well and allows to setup many bridges. It’s open-source, but the main benefit is that it’s also an open standard, like email. So you can use different clients and simply connect to the Matrix network it uses. Signal would be another privacy friendly alternative, but it’s even worse than Discord since it only allows one channel. Element can create a community, with multiple channels. Basically like Discord. It can be linked up with things like Jitsi to create video/voice calls, just like the forum. At work we use this combination as well. Easy to linkup with Gitlab as well and other tools (including Discourse).
But i’m getting off topic here 
I do think the movement stagnated because of the islands we created. Also this proposal of yours. Will you post it in the dozens of Facebook groups and whatnot? And then keep track of all those discussions in multiple places? Where some ideas are not shared with other people that are interested? An effective community utilizes a group mind. TZM has a split brain
Of course content creation is needed. But where are you going to post it for the maximum momentum? The TZM Global Facebook page is I think the #1 place for that. But it’s only controlled by a few people. And things are not always posted when requested. In effect handicapping the group mind. I think the clustering makes most sense for chapters, which operate locally anyway. But the main discourse should I think take place on Discourse 
It also has a builtin digest option that people receive if they don’t login. In effect proactively keeping people informed and perhaps also engaged.
Well, what do you know about what other chapters did? Perhaps it’s because we’re not communicating? 
The activism in Australia you listed in your proposal for example are really great! But I’ve never heard of it before… It could’ve inspired other chapters
But let’s see how it goes. Once I’ve freed up more personal time, I’ll finally be able to work on my content creation projects. Then the challenge becomes, how to reach the critical mass effectively…