I have a Note 9 that has a fault in the camera where there's little black floaties on the image but the lens is clean and un-damaged. My plan is due to run out in September so I only have around $300 left on my device repayments.
Seeing as the phone is still in warranty is it stupid of me to hope they'd cancel my plan early and put me on a new one instead of sending it off for repairs which will probably cost just as much as paying out my plan?
It's not stupid but it's very unlikely. The way you've put it makes sense but there are a lot more factors at play and whenever you add grey area to things like this for an organisation as big as Optus, things get very messy and what you're suggesting is definitely a grey area.
Tl;Dr not going to happen