Hi Paul,
Strangely enough I filed the feature request for this a bit ago:
https://tools.cisco.com/bugsearch/bug/CSCuq42355
and in TC7.3.3 it looks like the vendor class is now unified across codec generations (EX, C, MX-gen1 and newer SX, MX-gen2) and comes out as
Vendor class identifier: Cisco:Codec:1.0
And just to test, this is the case on my EX90 running TC7.3.3 in its DHCP request:

-Jonathan