Tested and working as of 1.11

These are some tileable & flush double piston extenders, using the 1.11 observer blocks. I made 3 designs. A flush with the floor design, a flush with the wall design, and a flush with the ceiling design. Some of the designs are listed as 2 wide because there are 2 slightly different designs next to each other.

The flush with the floor design is 2x4x5. It is somewhat based on another design I saw that didn't use observer blocks, but I am not sure who made the original design.

The flush with the wall design is 1x5x4 (1x5x5 if you include the redstone you would connect to the input). It is somewhat based on a non-tileable design that I think was made by Mumbo Jumbo.

The flush with the ceiling design is 2x4x4.