Hello,
We do plan to fully migrate to PSA APIs for cryptography. This means we'll retire mbedtls_md and mbedtls_cipher. The status of mbedtls_pk is still a little unclear because it does key parsing/writing, which PSA doesn't do; it might move to the x509 library since the supported key formats are mostly those used in X.509, or we may expand the PSA API to have similar functions.
It's highly likely that mbedtls_md and mbedtls_cipher won't be in Mbed TLS 5.0. It's not completely clear to me whether they'll be in Mbed TLS 4.0: they might be still available as a deprecated compatibility layer, depending on how much user demand there is.
Low-level crypto APIs (aes.h, ecp.h, …) will definitely not be in the public API of Mbed TLS 4.0, and ALT interfaces will no longer be supported.
Best regards,