So according to the RULES, the following are all legal 3x3 blasts:
Where do the rules say a blast can be anything but square?
Don't tell me they don't say it
can't; it's not the WotC authors' responsibility to account for every possible misinterpretation. Rather, they provide a straightforward definition, two similar features in the rules specifically and absolutely deny diagonal shapes (bursts cannot be diagonal due to the definition, walls
in the text disallow diagonal steps), and they give PICTURES of what blasts look like. "Here is a blast. Let us show you them."
Furthermore, I have repeatedly demonstrated why the diamond figure is not a 3 by 3 area. It contains squares that correspond to none of the 3 defined squares on either side. In reality, if you count across diagonally, you are encompassing a total of 5 squares, that's how you get 5 from "corner" to "corner." As others have indicated, what you actually have is the original 3x3 square with 4 squares tacked onto the sides. That's not a rotation, it's an expansion.
The rhombus shape seems a great idea for a houserule, as it maintains the spell area.
But just for exercise:
What is the maximum number of minions that can be killed by a 10 x 10 blast?