The mothering aspect is a must, yes, as well as Wendy and Peter's relationship with each other, but it's easier for me to think of what NOT to have than what to have.
Two things in particular come to mind as what NOT to have: the "living shadow" and the "flying pirate ship." Neither comes from Barrie and neither makes sense even according to Barrie's own rules.
Personally, though, what I'd like to see in a Peter Pan movie is a "subjective" Peter Pan. In other words, depending on who encounters him and what they think of him, Peter is different. So for example he'd start out like a demonic threat (as Mrs. Darling sees him), but then turn into a charming, cocky boy (as Wendy sees him), and then as a leader to be both admired and feared (as the Lost Boys see him), and as an irritating menace (as Hook sees him).
I think that's a rather Barrie-ish notion, and would aid in the mystique of the Peter Pan character. I still don't imagine any particular boy (not even Jeremy Sumpter) when I think of Peter Pan.