That's blatantly wrong. IPFS supports 25 different base representations (https://github.com/multiformats/multibase/blob/master/multib...).
In fact, recently, two community members decided to implement a new base encoding with emojis for fun:
https://cid.ipfs.tech/#%F0%9F%9A%80%F0%9F%AA%90%E2%AD%90%F0%...
https://github.com/multiformats/multihash supports at the very least SHA1 SHA2-256 SHA2-512 SHA3/Keccak Blake2b-256/Blake2b-512/Blake2s-128/Blake2s-256 Blake3 and Strobe. Hashes in IPFS are being standardised through the IETF and W3C https://www.ietf.org/id/draft-multiformats-multihash-05.html.
If you need rhash, you are welcome to submit a PR! We also have a grants program you can use to be rewarded for this.