I don’t think Malcolm can have a redemption arc. Even before he became Peter Pan, he was a selfish git who screwed up his life and his family – I mean, we can read between the lines of that episode. Mother Stiltskin left early on is my guess, sick of her husband spending all their money on grog and gambling (I have sympathy!) And Rumple, even though he was young, knew that his father was a feckless wastrel.
Yet Malcolm didn’t care. Given a magic bean, it wasn’t even let’s go to another realm where we can start again, it was let’s go to this place I went as a kid in my dreams where we can eat chocolate cake all day and fly. It’s all about him and his desires, not Rumple and Rumple’s needs which should be coming first as a parent (cf: Snowing putting Emma in the cupboard, even though it meant spending a lifetime apart, because it would keep her alive and break the curse)
You can’t redeem from that level of narcissistic selfishness. Not quickly. Unless Malcolm is going to be a recurring character for seasons upon seasons, he can’t have a redemption arc that is believable. And I don’t think he should. An integral part of fairytales have always been a lesson about morality – whether it’s tinged with religion or not (and I hope it’s not on OUAT), there is a lesson about acceptable behaviour in all fables and fairytales. Malcolm’s should be that if you put yourself first all the time and bugger the consequences, you’ll die alone and despised by all.