as per https://docs.microsoft.com/en-us/azure/virtual-machines/linux/mac-create-ssh-keys
'Azure currently supports SSH protocol 2 (SSH-2) RSA public-private key pairs with a minimum length of 2048 bits. Other key formats such as ED25519 and ECDSA are not supported.'

As ED25519 standard is more and more popular, also faster, more secure and supported out of the box on likes of Ubuntu and other platforms using latest OpenSSH it would be very handy addition.