I think at some point you're going to have to present an argument that user-serviceable RAM makes a perceptible difference in making the laptop thin/light going forward. Several assumptions - The RAM itself can't shrink or be made to be more energy efficient, or socket design is static, can be challenged. However a manufacturer without a mandate/incentive will probably never invest their efforts to making that happen. They're going to optimize for the commercial aspect of selling the product in a way that maximizes their bottom line via market segmentation and price gouging on storage. Obviously, making money is not something that I'm against, but I simply would like to see an acceptable compromise made between making money and making it repair-friendly. Like you said, everything is a trade-off.

Introducing a constraint like this, however, motivates the manufacturers to innovate making user-replaceable parts better instead of discarding the entire concept just because they can.