To be fair, the case wasn't proprietary and neither was any of the hardware. That's the one thing they got right with those. However, the power supplies had an anemic output rating which was not only low, but wishful thinking on the manufacturers part. You can't do much with a 200w or less PSU. You'd basically have to replace the power supply at a minimum before doing anything else with it.
At least it was possible. Dell, HP, etc. were far worse despite being better built. You had to keep buying proprietary nonsense outside of warranty and your upgrade path was far more limited.
To be clear, I think its possible to build a mouse that may last forever functionally. However, it would probably cost a lot and a subscription to go along with it is simply too much to ask. I don't know about you, but I'm sick of subscriptions, contracts and other monthly BS for everything now.