Personally I think spear saurus are still crucial, the parry bonus is statistically half as good as the +1 armor save we used to get if you are fighting things that are str 3. I feel that Saurus are really best at fighting light infantry, and ream fast cav of any kind rather badly. With the capacity for light infantry to be more effective in the new edition, I feel that saurus will still need to be on the table, though in what numbers I don't know.
I think there may be a definite need for some non-spear saurus, especially in a group of 12, just to provide their regular beat down and deal with lighter problems.
I think there is a place for a 30 man unit that's six wide and five deep. Probably need a few of both, honestly.
I can't think of a single unit in the Lizardman codex that became useless in the new edition, not even engine of the gods. In fact, with more shooting, it's gungan bubble is now more useful, making heavens easier to cast is still useful, and Burning alignment is still good since even though they are not as devastating, I think blood knights and chaos knights are still gonna be taken. Weathering a bunch of attacks back isn't hard when you're T4 and 2+ or 1+ armor. A unit of blood knights can just kill an entire unit one by one if it has too.