First, I love this change where smaller block shapes have less HP. I've wanted that since forever, and I don't want to gloss over how awesome it is to have that now. Thank you, Gazz!
I don't really share Papa Legba's fear that this will reduce base diversity, because HP isn't the only consideration for a block's shape. Besides aesthetics, there are other properties to consider, including sight lines, what can penetrate, and how zombies move in the presence of a certain shape. Depending on the base design, the HP may not matter for a large majority of the blocks that make up the base.
I also anticipated long ago that the move to craft universal blocks that can take any shape would shut the door on material cost being proportional to the shape's size. But now that I'm thinking about it again, I guess the stack sizes are arbitrary. They could do the same thing they did for meat and gas: scale up the numbers enough that you don't need fractions of a unit. Placing a full block depletes your stack of building material by 4 units. Placing a half block or ramp depletes it by 2 units. Placing a pole shape depletes it by 1 unit.
The other common sense quality that different shapes could have is smaller shapes having less structural strength than larger shapes. Although given my druthers, I'd rather see structural integrity depend on a block's rotation. E.g. you should only be able to attach a block to a plate or sheet shape on one side. This would cut out a large class of floating base nonsense.