It would be nice to be able to use non-numeric Feature Codes in Feature Code Admin, maybe via a setting (e.g. ALLOWNONNUMERICFC in the old "amportal.com world") that defaults to the old behaviour.
I agree that this is not needed for normal use of feature codes, but would be cool to have for codes that are only sent from the phones (e.g. I would be able to use "cf" and "dnd" Feature Codes that could be used when the respective feature is enabled on the phone and would be handled by my home-made silent CF and DND modules. ...and maybe there are other uses for this, too...)
This is currently checked in the js-function frmAdmin_onsubmit() inside page.featurecodeadmin.php using the js-Function isDialDigits().
P.S.: Technically, it seems to be possible to use alpha(numeric) extensions in Asterisk, but there seems to be a length limit or something when using them together with patterns.