The initial test involves "over 100" government and first responder Pages, and will be capped at 35 alerts over a rolling 30-day period to prevent overuse. Also, Facebook is adamant that this isn't meant to replace conventional emergency alerts. It's there as an additional, more convenient source of information.
You should also find the Today In section in more places. It's available in 400 cities in the US and just launched in Australia, but you'll now see Facebook test the feature in "news deserts" where there are few sources of local information. In these places, you'll see the company supplement what local news there is with material from surrounding regions. Think of it as local-ish news.
The expansion is part of Facebook's larger strategy to fight fake news, in this case by promoting local news and other, more trustworthy sources of information. Whether or not it works isn't clear (a lot of this is voluntary), but it might just encourage local engagement at a time when national news tends to dominate the media landscape.