Hello,
1) In regards to Summer Hinata, Why do you say she was supposed to be the sign in ninja, then was replaced?
We already had her as a Fireworks ninja, so it's unlikely we will get her as a Fireworks ninja again, and getting her as a Myoboku ninja after getting her as a Fireworks ninja is also somewhat repetitive. It would breed the same kind of complaints people have about, say, Suit Minato or Swimsuit Omoi or Halloweed Kabuto.

2) In regards to Itachi Anbu,
He is certainly not a meta ninja, and he certainly falls within the power level for a Fireworks ninja, but having already been given away for free within a monthly sign-in, there are many other ninjas to be given away in a sign-in, fireworks festival event, or Myoboku Trial event than a ninja that has already been given away once. As mentioned, many players would complain to see a ninja in one of these events being given away again.

I will put your suggestions in, but please be aware that there are many others with competing suggestions that will not like this, so the suggestions may not come to fruition.
Would you like for Itachi Anbu and Summer Hinata to instead be available through events? You mention collecting fragments. That might be an easier route for you.