The smart move is to start Keenum game 1.
He's earned it. He's played very well. He's earned his teammates and his coaches respect.

If he flops nothing could be more welcome by everyone than to insert Goff.
If he succeeds, that works, too.....nobody will complain and all will be happy for Keenum. The Rams will be seen as having untold riches at QB.

But....if Fisher starts Goff in game 1, and in a couple of games Goff is shaky (whether its truly his fault or not) and he has to insert Keenum, that is going to be a headline for the rest of the year. And, it is going to hang around Goff's and Fisher's neck for a long time.

Granted, if Goff goes gang busters, great. But of all the possible outcomes, it is far less risky to start Keenum game 1 and let it play out. After all, both Fisher and Snead have been saying publicly for the last few weeks that if they had Keenum the last couple of years they'd have been in the playoffs.