In this alternate history, Tawantinsuyo resisted all attempts at conquest. The reason is not very important; let's say a fluke storm killed all of Pizarro's men shortly after they started engaging the Inca, who, magically resistant to all Old World disease, adapted to modern weaponry rapidly. Any subsequent invasions they held off valiantly, and the shared enemy coalesced their previously divided nation into a cohesive, centralised country. The centuries passed, and over time they modernised with the rest of the world. Assume there was never any specific period of isolation; they had friendly and not so friendly contacts throughout the ages, they were just never conquered.
Now, in our history, the Inca had no conventional system of writing, in the sense of inscriptions or markings that can be read. Instead, they used a system of knotted threads called the Quipu for administration, and possibly, communication. They looked like this:
Now, debate is ongoing over whether this system was phonemic or not. I am going to assume that it was phonemic, or that it became that shortly after its use diminished in our timeline.
So, assume that you can "write" everything using quipu. It has native representation for every sound, and thus everything you want to say. Imagine it can do anything our writing does, except it is made of rope.
My question is: would the Inca ever, between the 1530s and the 1990s when computers became commonplace, have needed to use paper notation and thus a standard script? Obviously Inca translators would have needed to figure out alphabets of other tongues, but I am talking native use, by administrators and peasants alike. Assuming that a quipu can represent anything a more conventional writing system can, is there any practical issue with writing with rope that paper does not have?