It's still in ruby, although I see the new GUI is in swift: https://github.com/homebrew

Rewriting a program in Rust (specifically) really only makes sense for a few reasons:

1) the existing implementation is in an unsafe, cumbersome language (C, C++).

2) the existing implementation language is too slow and that slowness cannot be worked around.

3) the implementation is enormous, in a dynamic language and you desperately need stricter types. But this doesn't really favor Rust specifically.

1 doesn't apply because Ruby is garbage collected. It's doubtful 2 applies just given what homebrew does: the long pole is always going to be I/O. The performance improvements in version 7 seem to mostly be due to doing more concurrently. I highly doubt the Ruby-ness gets meaningfully in the way.