Yes, I think that would cover most cases if we take it to its logical conclusion of wiping all device state (hard disk). OTOH, a few points:
1. I would accept the need to wipe the hard disk if I had messed with firmware or the OS, but not if a couple of keys on the keyboard had stopped working. This implies that (for me at least) a meaningful distinction remains between these two "levels" of warranty service. Do you agree?
2. Activities like overclocking or overvolting a CPU have the potential to cause lasting damage that can't be reversed by re-flashing. Under the policy you're suggesting, it would be illegal for manufacturers to offer users the option "You can pull this pin low to overclock outside the supported range, but you will void the warranty by doing so", and too expensive for them to endlessly replace parts damaged by these activities for free under warranty, so that consumer option, rare as it already is, would go away completely.
3. I still think there may be some devices that are impractical to completely re-flash. According to this 2021 Porsche article [0], modern cars contain 70-100 ECUs (microcontrollers), each of which will have its own flash/EEPROM.
[0]: https://medium.com/next-level-german-engineering/porsche-fut...
1. I expect wiping any given component to be entirely up to the manufacturer's discretion. If doing so is not trivial and is legitimately required for the repair to proceed then I'd expect the user to be charged for the additional service.
2. Violating manufacturer specifications and being at fault for damages are sometimes distinct. A manufacturer arbitrarily saying "you must not do X" should not necessarily mean that doing X will void the warranty. It might though. Discretion is obviously required.
3. If your car stops working after you mess with the firmware and you take it in to the dealer I imagine they'd charge you to reflash things since the issue was caused by your own actions. That doesn't mean they should be able to decline to cover entirely unrelated defects.
Also I don't think vehicle firmware would be caught up by the original proposal in the first place since cars aren't generally intended to run third party software. There's a grey area with infotainment systems that have an app store depending on if those are viewed as standalone or part of the larger vehicle. However reframing the proposal to revolve around intent would likely leave the firmware on unrelated embedded components in the clear to be locked down so long as those components don't interfere with the ability to freely use the general purpose computing element.
Personally I'd like vehicle firmware to be covered by similar protections but I recognize that falls outside the scope of a proposal about products intended for use as general purpose computing devices.
I don't like the "intended for general purpose computing" concept so much. For one, it seems to offer lots of easy wiggle room to manufacturers: Just say that your product is not intended for that, but for something marginally more specific. For another, it's not clear to me why general purpose computing ought to enjoy consumer protections that other manufactured devices do not. (One exception I'd grant is for safety reasons: If tinkering with a device could make it cause injury, fine, that device can be in a different class.)
There might be a couple messy edge cases if applied at the software level but I think it would work well.
Applied at the hardware level it would be very clear cut. It would simply outlaw technical measures taken to prevent the user from installing an arbitrary OS on the device.
Regarding warranties, what's so difficult about flashing a stock image to a device being serviced? At least in the US wasn't this already settled long ago by Magnuson-Moss? https://en.wikipedia.org/wiki/Magnuson%E2%80%93Moss_Warranty...