HOW LUFFY INHERITED ROGER’S WILL

Okay, so, we all know that Luffy inherited Roger’s will, but how does inheriting will actually work? And at what point in the story did Luffy inherit Roger’s will and how?

This is my speculation:
Did you manage to catch what was the reason Shanks gave up an arm for Luffy and gave him his hat? It happened right after Luffy ate the Devil Fruit Shanks was carrying. After eating the fruit, Luffy showed a lot of similar traits with Roger. Before eating the Devil Fruit, Luffy never once mentioned that he wants to be the Pirate King. So, the way Luffy inherited Roger’s will is eating a Devil Fruit. But how exactly does that work?

Well, take Sabo for instance. Upon eating Mera Mera no Mi, he said that he will now inherit Ace’s will. That could mean two things:
1. Roger was a Gomu Gomu no Mi user (I don’t like the idea of that)
2. There are other ways to inherit someone’s will via Devil Fruit

In first case, it means that every Gomu Gomu no Mi user shares treats with the original Gomu Gomu no Mi user
However, in second case, it opens up a possibility of storing one’s soul into a Devil Fruit.

But why would Roger choose Gomu Gomu no Mi out of all Devil Fruits? I believe it is because of Goro Goro no Mi. However, all that stuff is pure guessing.

We haven’t seen Devil Fruit eating in action a lot of time, but after some time, the Devil Fruit user’s personality changes in a way.
Now, I don’t believe Roger had any DF because of the crew’s reaction to finding Devil Fruit, they percieved DFs as something strange, not as something they are familiar with. I believe Devil Fruits aren’t anything old – they were created in last 50 years or so. (maybe Uranus or national treasure of Mariejois, who knows)

I’d like to see your opinions on this.

*Theory by JewDoo