As mentioned, there's a draft to collect and 'fix' problems that we
(google netops folks) see with tacacs+ today:
<https://tools.ietf.org/html/draft-dahm-opsawg-tacacs-01>
If folk can give this a quick read, send comments to the authors (see
draft for emails of authors) OR the ops area wg list:
<https://mailarchive.ietf.org/arch/search/?email_list=opsawg>
that would be good... even better if you find your favorite vendor
critters and ask them their plans in this area.
Someone asked, in the meeting, about: "What about key auth?"
that sounds like a great thing to take up with Thorsten and Andrej 
-chris