Current GCM implementation seems to be buggy - rfc test vectors for GCM partially fail - it will need some more investigation.

Is it this feature going to be implemented some day?

IV is mostly a common practice in the industry for encryption with AES-256-CBC cipher.

It makes also hard to migrate from MySQL to MariaDB due the lack of this function.

yes

Is there already a new time schedule or version? We are also eagerly waiting for this.

MySQL implements

AES_ENCRYPT(str, key_str [,init_vector [,kdf_name [,salt [,info | iterations]]]])

with 6 positional arguments this is, I think, way out of comfort usage zone. And it does not allow to specify the mode, it has to be specified via block_encryption_mode variable. I would rather suggest

AES_ENCRYPT(str, key [,iv] [USING mode])

2- and 3-argument syntax is compatible with MySQL. Encryption mode is specified via a keyword, so it won't cause ambiguities if we'll later want to add full MySQL compatibility syntax.
But I think it'd be more user-friendly to add a separate function, say,

KDF(key_str [, kdf_name [, salt [, info | iterations]]])

which is not part of this task

On the other hand, the syntax without a keyword will make it a normal function with no special rules in the parser. And the server will still be able avoid ambiguities because kdf values differ from mode values.