This is backwards. Google rescued Deja’s archives which were going to be deleted and then expanded the archives back to 1981. Without Google’s interventions you’d all be left wondering what was in Usenet.
I've searched for some of my old posts from the early 90's onwards (mostly in non-controversial political discussions and comp.*), they're not there. It seems to be a selective archive. It's verging on impossible to find anything meaningful.
One thought that I have had is, would NNTP nowadays be a good place for discussion? There are still news servers (mainly used for piracy last I remember), but maybe September has actually ended in Usenet given that all the 12 year olds have moved on to facebook.