I don't think Neville will kill Voldemort. He doesn't have the power. At most he might strike a blow that distracts or weakens Voldemort slightly, setting him up for the death strike.
I think that Harry will try to kill Voldemort and fail, possibly due to their wands having the same core, and that Voldemort will think he's won.
And just when all hope is lost, Professor Snape, the greatest of occulumens, will strike, killing Voldemort and avenging Lily's death.
Because Snape loved Lily, which is why telling Voldemort the prophecy that led the Dark Lord to kill James and Lily was the greatest regret of Snape's life.
Only love kills the demon.
Interesting thoughts on Snape, being the one who finally kills LV.
But I'd like to remind you that when Neville was in Dumbledore's Army, he was getting better and better. And he and Luna are in the Ministry with Harry when Harry thinks his Uncle Sirius has been captured by LV.
Remember, Neville was born in July, at the end of the month.
I'm not so sure that something isn't going to happen in book 7, where neville finds that Bellatrix tortured Neville's parents at specific direction of LV, or even that LV was involved, and he's going to find his backbone, and for the love of his parents, it's his wand that is doing to do in LV.
Isn't Neville's the "last wand" that Olivander sold?
There's more significance to Neville than we've been told about, I'm sure. He isn't the little wussy anymore.