I've thought about this as well. The first thing that comes to mind when envisioning a Surf Coaster is the position you'd be riding in. It would be the exact opposite of the way you board and ride a B&M flying coaster - instead of the track being above your head with your body sprawled out in flying position, you'd be riding above the track with your body stretched across a flat platform. While this idea of mine would require long stations for high capacity, it'd also possibly enable these coasters to be more compact than any other. Most B&M coaster trains have a height of 4-10 feet, whereas these would probably only be 4 feet and under; therefore, track clearance requirements would be much lower when compared to other B&M coaster models. I'm very excited to see how this develops over the coming weeks, months and years.Long overdue if it is! It's about time they came up with something new to compete with the rest of the market.
As for the kind of coaster, it sounds like a water coaster to me, or at least a coaster that involves water in some way.