I'd be down for a Brightline and Tri-Rail route. I think the soon-to-be-open Orlando route would be a real blast.
Probably because it's cheaper/easier to build for expanded service proactively, rather than have to pay out the nose later on and jump through hoops for new permits? Not to mention some stations share service with Amtrak. It's better to have and not need, than need and not have.