Generally, and this is just my gut feeling, I think that for any hash code written to disk or stored in some way having an identifier for the hashing algorithm used is such a common bite you in the ass later thing that it makes sense to always just do it from day one. To that end it’s easier to do day one if everyone agrees to a standard set of numeric codes.
Multihash is the standard set of numeric codes for different algorithms I am aware of.
Unifying here might allow git objects to be served natively over IPFS.