Ask HN: Android OS with Linux level customisation

Hello HN, I've been working with Android from the past few weeks and I have noticed that android is nowhere near customisable like linux. So I've decided to develop a custom ROM that has exactly this. A fully customizable android with linux level customization. Before I even start this project what are the most technician limitations for this project? Why has noone done this before? I would love to see critiques and why this doesn't work , I'm still learning android so I'm not too sure why it might not work. Thanks!