It’s been some time, since I’ve last followed up on this conversation, sorry for being late to the party but allow me to share my two cents on this:
I think (at least a good part of) the community has adopted Telegram pretty much okay. I’m not saying it doesn’t have any drawbacks - it has plenty, but is a good place for overall communication, and is polished in ways that’s rather easy to overlook (and this polish goes a long way in enabling the ease of communication).
Also people above taunting Telegram or IRC make it seem like we could just, with a flick of a switch, migrate all the people magically to Matrix (or any other system we decided on using as the “one true open source solution for mozillians’ communication”). I know most of you did not mean it that way, but this might be how people reading this take this, and that’s just not true.
All systems have their own momentum, it will be hard to herd people to any other system, be that from IRC or Telegram. I think the proper glues and connections are invaluable here - and that’s a good point for Matrix, for sure, being open source, and thus, hopefully, highly customizable.
The Telegram bot we were using in the Reps telegram channel solved a lot of the problems (not all, certainly), with more customizations it could solve even more - but that wouldn’t solve the inherent issues in IRC, which was used for the “backend”, or rather, Nexus of conversations happening in Telegram.
I have absolutely no problem with using Matrix as the said nexus where all other channels converge (its mentioned malleability surely helps putting the required glues in place), but I expect that to be more a nexus (such nexus that Slack actually tries to be), at least for a few years, which consumes all the content from other channels (looking at IRC, Telegram, Discourse even), aggregating and storing them (for posterity) in a single central location. On the long term, I can imagine the UX and the inherent pros of Matrix sucking away most of the users from other channels/services (but I’d imagine this would take several years and really excellent UX & performance work to happen on the clients & servers alike), but those glues need to be set in place nevertheless so the conversations are actually less, rather than more fragmented with the introduction of this new system (and we do not fall to prey the Standards-creep, as per this XKCD-classic).
What this means, is I think before any migration could possibly be happening, we need to hose (ideally in a bi-directional way) other channels - IRC and Telegram at a minimum - to this new system.