Good to know, it never sat right with me that Guile depended on BDW-GC for so long. That's what you use when you are implementing a toy language and don't have time to write your own GC.
It was never the biggest hurdle for guile performance. I do believe guix has the potential to hit the GC wall, but for most programs I think it has served guile well.
With that said, the upcoming immix collector is really friggin exciting.