Short answer: It'd be a little tricky, or a lot sloppy, but is doable.
Long answer: The data is not stored "in" the template. The database is stored exactly as you see it when you edit your page. It's when you call that page that the wiki renders all of that information, and calls whatever templates are in use. This means there's no table that holds all the people using all the templates, all the data they've entered, etc.
How I'd do it is essentially specify the variable, then trim everything before the variable. Then look for the next pipe, and trim everything after it. I'd have to do a little more studying on SQLing to get that going, but it think the concept is sound.
As for +events, I could see a few ways of easily doing it. Output the data from the MU into an SQL table, then have MediaWiki query the table on demand. It looks like there's a few options ( https://www.mediawiki.org/wiki/Extension:SQL2Wiki ) but they are all flagged as dangerous, or a security risk, because you are meddling with the database. I'm not sure if it's possible to lock an extension down in a way that it only functions when an admin type is the one to first use it.
All in all, it looks possible. Personally, I wouldn't have time to think any harder about this for at least a week.