Looks like a good idea!
Keep in mind that the larger blocks, you'll lose some of your 4PP as you'll be chopping off the corners with the trellis twist piece. With the two different sizes, you could do a smaller 4PP for the small blocks ... or use the original fabric.
Another similar one is my Double Rose Trellis pattern. You can have a look at it here.
http://www.quiltingboard.com/t-122204-1.htm