I really enjoyed this story. Love Powerful Grey Harry. I am a big fan of the time travel and alternate dimension stories and found this very enjoyable.
Maybe for your next one, you have Harry end up in a dimension where Neville is the BWL, but incompetent. James and Lily are still alive (and not insane, because unlike the Longbottoms in canon. Sirius and Remus are there to help take down Bella and Co.) The higher powers realize that Neville doesn't have it in him to do the job alone and so send an adult Harry to merge with his 11 year old self.
It would be interesting to see Harry with brothers and sisters.