The current status of ‘wip-grafts’ is that it works, there’s no
performance issue, etc.

However, the ‘graft-derivation’ procedure is not recursive: it grafts
the derivation you give it, but doesn’t graft its dependencies.  Thus,
only direct references are grafted, which isn’t so great:

  $ guix gc -R $(guix build glib) | grep bash
  /gnu/store/8fmgslrivicy54azysmaab3z1srid773-bash-4.3.27  <--+--- the ungrafted bash
  /gnu/store/3yiqz9wmwx6b7hpbapg5q39sjx33kh0j-bash-4.3.27  <--’
  /gnu/store/yl1rp2b8i2qwgxja3d09xc24ffk9sjmr-bash-4.3.27  <------ the grafted bash

Changing ‘graft-derivation’ to work recursively and perform well is a
bit challenging.

I’m posting the naive patch I have here, in case someone can look at it
before me.

Ludo’.