You'll end up with a portable desktop with bad thermals, impacting performance, battery life, and actually-on-the-lap comfort. Bleeding-edge performance laptops can really only manage an hour, max, on battery, making the form factor much more about moving between different pre-planned, desk-oriented work locations.

I take my laptop back and forth from home to work. At work, I ban them from in-person meetings because I want people to actually pay attention to the meeting. In both locations where I use the computer, I have a monitor, keyboard, and mouse I'm plugging in via a dock. That makes the built-in battery and I/O redundant. I think I would rather have a lower-powered, high-battery, ultra portable laptop remoting into the desktop for the few times I bring my computer to in-person meetings for demos.

I wish the memory bandwidth for eGPUs was better.