Lauda's crash and recovery makes one good story line, and so do Hunt's "interresting" way of life, but I'm affraid it leaves a certain void in the scenario.
I just hope they won't fill that void by enhancing a special "rivalry" aspect that just wasn't there. Correct me if I'm wrong(and I could well be wrong, I wasn't born yet back then), but Hunt and Lauda weren't bitter enemies. Both had very different styles, and both were very emblematic personalities in the F1 paddock, but that's about all. Theye never had any controversial incidents between each other, and they didn't even get to fight against each other on the long term - 1976 was the only year thet went head-to-head for the F1 championship.
Very far from the Prost vs Senna, Piquet vs Mansell, or even the Schumacher vs Hill rivalries, for example.
That said, making films out of real historic events can be pretty hard to do, if you wish to remain accurate. This is why I'm surprised they didn't just decide to just go the easy way and stick with a fictionnal scenario, still based on the mid-1970s era. But anyway, best of luck to them.