You can now find a cave of dark blobs in the railsystem. It's somewhat small, but given the amount of dark blobs in the rest of the railsystem and the lack of frequency the rest of the new baddy areas have gotten I'm not exactly sure it's necessary to make it larger.
But if there are complaints I can expand.
BTW if people haven't realized, cave-ins were never intended to be able to be blown up. They have always represented caves that can't be accessed. It's the cracked walls you're looking for, I see a lot of players constantly try to blow up caved-in entrances.