I doubt they'll bring back the cheese grater. But it will likely be a tower of some sort.
I think a tower is extremely unlikely. The quotes is interesting in that they were banking on multi-GPU and instead it's single über GPU but the latter is the reality. I'll be surprised and disappointed if they return to a tower. I'm really hoping for an eGPU solution. Get the GPU removed entirely and isolate it and potentially come up with some way of handling SLI connections externally.
Going back to a tower just seems like a step in the wrong direction. Furthermore, they're pretty clear about Pro users liking laptops. I use one. Something external means the component is available across their product lineup. It seems like a product makes more fiscal sense if it's something that can be used by more people than just Mac Pro users. I think it's pretty clear at this point that they're Apple's smallest device demographic.
If they were going back to a tower, there's no reason to wait another year.
Looks like the Trash Can is basically just the the G4 Cube v2.
Overall this announcement is exciting, even as someone with no interest in a Mac Pro. As a Mac user there's reason to feel uneasy about the future and this announcement helps rest that a bit.