I actually believe that Draco's offer of friendship at the beginning was sincere. Although I suppose that could be open to interpretation.

The key would be how would this have gone if it were written in canon. Meaning, inevitably, Draco and Harry would have a disagreement, likely a fairly significant one, and that would have the potential to end their friendship.

However, by that point it will be too late. Harry will already be sorted into Slytherin and he already will have openly accepted Draco's offer of friendship in front of their entire year. He, unfortunately, will probably have ruined his chances of being friends with the others. Anything is possible, though, of course.