Beautiful 4PPs!
First of all, I'd love to see the virgin fabric used to make them.
If you could post a pic, I'd sure appreciate it.
As for expansion ... there is always the possibility of making more 4PPs if you have the fabric. As a switch, you could put them on point with more of your sashing material between, or another coordinating fabric. Or instead of 4PPs, make hexie or octagonal kaleidos.
Likewise, it is not uncommon to use the virgin fabric for borders.
Of course, there's always other coordinating fabrics that could be used for borders.