DIY EFI had the leasn cruise working on GM V8's a couple years back. IIRC, they cycled it on/off so as not to get things too hot running too lean too long.
I'm not sure of all the specifics but I thought that the stock code took care of the cycling. I seem to recall reading a description where the the O2 sensor was "put to sleep" during a steady state cruise and would wake up from time to time. Interesting concept anyway. I'm going to enable mine once I get the ECU tuned.
No, as I recall hearing it, the code was there but it never gets to it. Essentially its disabled. I haven't followed that list for a while, but when I did, a couple years ago, there were people trying to implement it.