I think the biggest group of cars I would never expect to return are the majority of 1998 everyday road cars from GT2 and early 2000s everyday road cars from GT4.
Basically the Qashqais of their day - cars that got into the series pretty much only because they were new on forecourts at the time. Obviously a few are still noteworthy and might make it back one day, but I really doubt that, say, the Mini One is ever coming back.