For once, no hardcoded tweet/toot limit. The only limitation would be the network - the ability for toots to leave the home instance as they're pushed to other instances.

Given the current size of mastodon.social (the largest Mastodon instance) and its ability to push toots out to other instances (including mine) despite the size of m.s, I don't think it would be an issue in the current circumstances.

If something less obtrusive is wanted, a simple push notification or webpage?

I think the best approach is to still use Twitter but also use all Social Media like Facebook (especially), Insta (hard to do for text) but you could link to their Website with the same posts/info.

In the end you have to try and inform the public where they are, just like would happen on TV or Radio in the past.

Maybe it is actually a space for Google/Apple/Microsoft/Linux as OS makers to provide some functionality to do this kind of broadcasting over the internet in addition to working with Telcos for SMS/mobile based alerting.

Isn’t this the emergency alert notification? Or are you imagining something for situations where it isn’t an emergency but the information needs to be out there? If so, I’d be thinking a dedicated app is what’s needed.