What do you want to see from Sam in the sequel?
The main thing I loved about Sam in the first movie was that he was this little demonic trick or treater. His battle with Kreeg and punishment of Emma set him up as a cool new horror character. But there was more to Sam than that. In the other stories he appears as either an observer or maybe even the instigator of events. In these stories he doesn't actually do the killing/punishing himself but seems to be very interested if not directly involved, basically the enforcer of the rules of Halloween.
Having just read the new graphic novel written by Michael Dougherty and what I believe will be his writing partners on the sequel, it appears that they are going for the idea that Sam is in fact the spirit of Halloween. Why does Sam have to be the spirit of Halloween entirely, why not just concentrate on the trick or treat side of Halloween? In these new stories Sam is seen only as a spirit/vision who has looked the same since the 1600s. Why footy pajamas in 1640 Ireland? I guess for me if you are trying to say Sam is basically the god of Halloween he would not take the form of a costumed child through all time. The final story features a shrouded reaper type character that seems to be in charge. I like this idea much better, Sam being some trickster type who works for Death. I want to see Sam doing more mischievous prankster stuff and not just being some omnipotent presence.
When asked what I want from a sequel I don't really think an origin story is necessary. Michael Dougherty has recently said that he does not want to do an origin of Sam that he wants to keep him mysterious and I agree with that. But I do feel they need to decide if Sam is going to be the demonic trick or treating prankster or if he is some all-powerful spirit that observes and influences more than actually killing.