I've been over this before, but for posterity:
I'll implement/merge LayeredFS or some form of overlays, but RomFs is a no-go. I will not compromise on this.
Most games it would find use with are over 1GB, and the data which is modified is a small fraction of this, usually. The result is huge, ugly, awful, unneeded duplication of data.
As I don't have nearly as much time for Corbenik anymore, I've largely kept changes to bug fixes when problems arise. To be blunt, I'm unlikely to implement layeredFS on my own at this point. It's too much work for too little gain this late in the 3DS' lifespan in my opinion.