Actually, Shanks' sentence after this chapter makes sense to me
I sacrificed my hand for the future generation
He had to have this tattoo on his body and to remove it, he had to cut off his hand
And when Shanks' hand was cut off while Joy Boy was in his arms, Oda could play with this chapter and say that at that moment Shanks' regen was destroyed and his hand was cut off
That would be interesting