Ichigo isnt 1/4 quincy, he is not a hollow either. His hollow powers were made from his shinigami powers and it returned back when he used final getsuga. Thats why he fought aizen without hollow powers since it synced with his shinigami powers. So far we know that his spiritual energy had realised quincy powers. Do you remember back in the beginning when he got stabbed by a shinigami sword? A shinigami is born from the soul society. It cannot be given to someone else did you know that? Everyone in soul society believe that he holds rukia's power but they were shocked when he used bankai cause a borrowed power cannot awaken a bankai because its not his powers.
Just like that now his quincy power has awakened he is 1/2 shinigami and 1/2 quincy. His mother would either be a quincy or a shinigami and juhabach might just be his father. Think about ichigo's final getsuga which is used when he fully connects with his sword have you noticed his hairstyle? it resembles juhabach and also have you noticed old zangetsu also resembles juhabacha? Thats just my theory but it could be the other way around and isshin could still be his father.
A quincy borrows power from outside, a quincy is a human who is spiritually aware. The grim truth is that the boundary was not between hollow and shinigami but rather quincy and shinigami. Aizen could never become a quincy thats why he couldnt beat ichigo who was a hybrid. Ichigo is the most power being because he is more powerful than quincy and shinigami. It was the huge secret and people ignored the signs from the beginning. If you don't believe me watch the episodes when Uryu fights his own father you will notice that he regains his power when his dads shoots the arrow at him. The arrows is pierced through him similar to ichigo. The whole idea is aizen was testing ichigo to see if he could become a shinigami because "Offspring of both shinigami and_________"