Hard to really guess what would have happened but it's possible that a Chinese speaker could have opted to start with one of the romanization systems or zhuyin

Hard to really guess what would have happened but it's possible that a Chinese speaker could have opted to start with one of the romanization systems or zhuyin fuhao and then build a system to inputs characters at a later point. For Arabic the challenge is more akin to this type of problem: "create a computer that can handle a cursive form of the Latin alphabet". You could start with something really rudimentary like allow for Arabic characters in isolated form. It would be ugly and challenging to read, but a start. Wouldn't be too hard to add the initial, medial and final forms, eventually diacritics as well.