I don't think so. Letting the manufacturer decide which parts of a system "belong together" will not enable an effective repair, as companies like Apple will just say that their whole logic board is a single unit and to "repair" it you need to throw it out and get a new one (actually that's exactly what they are doing already by restricting repair shops from buying specific chips they use on their boards; many board problems would be easy to repair with the right 30 cent IC, Apple just won't let repair technicians have those). That's a bit too convenient maybe. A better approach would be to see what is practically possible in terms of repairability without significantly compromising other aspects of a design, and mandate this to everyone. Another way would be to create fore-runner programs, where the most innovative and efficient solution becomes the standard for everyone to follow. This worked well for products like cars so I don't see why this wouldn't work for computers.

Also, saying "if you don't like their limits then buy the other brand" is not a strong argument against standardization and regulation of technology, that stance would basically give a free pass to manufacturers to do anything as long as there is customer demand for it. Any industry that can produce significant external negative effects like waste or pollution, which are not primarily experienced by the consumers (think of pollution produced by cars; not very inconvenient to each individual consumer, but harmful to people in cities due to the large number of cars), needs to be regulated based on environmental and sustainability factors as well.

The ability to upgrade would be a bonus and usually comes automatically, if you have the ability to repair a device. OWC is well-known for offerings of upgrades for Apple computers, which were not officially upgradeable, as well as of course, repair kits, like for the battery in some models.

A right to repair should be one of the fundamental customer rights. In this case, not only protecting the customer, but also the environment. Customer rights exists for multiple reasons. First of all, to protect against undue forcing of customers into something. Even if a company doesn't have a monopoly in the strict sense, they might try to force you into situations, where you cannot just choose a different brand. Especially if all brands go on a similar course.