Anything is possible given enough time and/or money
It is much more complex than simply adding them, you have to add options for replace-all, only-modify-existing, only-add, only-remove, etc... as well as updating multiple entries for each lead being much more complex to program.
It's not a current feature because hardly anyone uses extended alt number dialing anymore. All of our clients that had been using it moved to MULTI_LEAD auto-alt dialing many years ago.