The only way to reach the "full potential of the i9" (meaning to run it as a 130Watt desktop CPU) is to put it into a significantly larger chassis. That simply won't happen with Apple. And I start getting tired of pointing out that the i9 on the MBP reaches all its advertised spec: it runs at 4.6Ghz single-core turbo and at or above 2.9Ghz multi-threaded. Yes, a large gaming laptop twice the size and weight will perform 20-30% better. If you are interested in that kind of machine, get a large workstation.
How do you know "That simply won't happen with Apple" releasing a MBP with a significantly larger chassis? Do you brunch with Tim Cook every weekend? With Apple letting users replace the battery in the Macbook Air, it seems Apple is somewhat open to criticism and making changes. Will they make a larger MBP with better cooling? I don't know, but can I at least hope they will?
I understand the i9 in the MBP I own is not a desktop and if I was looking for a workstation I would have bought one. I never said I wanted desktop performance in a laptop. However, when I'm rendering 4K video and I hear the fans blowing and my MBP gets really hot, I can see it's being throttled significantly. My argument is that I just want a larger chassis so we can get better cooling and longer sustained turbo. Just because it runs on it's "advertised spec" doesn't mean it can't run potentially better. Sorry if that makes you feel like pointing out how wrong I am.