My plc just set up a discord server and it is working out great. I'm not sure why but they communicate more when there's an app involved. It supports being goofy and limits it because they can only type so much.
As for making a huge scout server the idea sounds cool. Being able to make new friends in far away places is what ham radio is all about. You're just trying it with different technology. But I'm wondering about the details. With 100k users it might be hard to keep a thought in focus. Once in a while I watch this giraffe in NY and there's a stream of messages flowing on that I can't imagine anyone being able to comprehend. There's also the issue of people using it for reasons you don't want - spammers, trolls, phishing, etc. I think it can be solved but it is a big deal and it needs to be solved.
How about this: start small and grow it. Set it up, go to round table, announce it to the troops in your district. Let it grow. See what the problems are and fix them. Find other districts. Repeat. Picking districts far away from you could be a fun way to find out about new places to go on high adventure trips.
I'd be interested in knowing how it goes.