Ohh, I just tested this a bit. Works pretty much the way I was hoping for. Thanks!
Only thing I might bug ye about -- what are the relevant MediaWiki messages? The main one, I think, would be whatever indicates the page has been affected by cascading protection.
Hm, I also see that it shows up, when using &action=protect -- are there any other circumstances in which the cascading effect will be apparent? I'm mainly thinking of non-admins, here. Unless we're planning on using this infrequently enough that this isn't a major issue.
-Luna