That's (almost) the same screen size as the 12.9 inch iPad Pro, no?

Fair enough, it's close. But I still wouldn't do it. It would be like a carpenter bringing a screwdriver with a metal handle so he doesn't also have to bring a hammer.

I care about the tools I use to do the work I do and I don't want to compromise (or compromise very little). I don't think I can get serious work done on an iPad without faking it and saying, "um, sure, it's great!", and without honestly feeling claustrophobic.

Big and powerful dev setups are great, but that’s what my 42” 4K Dell monitor is for — and there’s no way that’s going to be portable.

So the reality is that there’s no such thing a no-compromise dev setup: Either you optimize for a desktop setup, or for portability, or somewhere in between. If you have the ability to have both a desktop and portable setup, such a pair I almost always going to be superior to just one medium sized laptop: Your desktop experience will be better with massive high resolution monitors, and your mobile experience will be better with a lighter, slimmer device and longer battery life etc.

I haven't said anything about desktop or big 42" monitors. I'm not going to give up my laptop for a tablet. This is just utterly ridiculous.

I absolutely prefer to have a larger external screen, too. But if I'm traveling, and the choice is between my 13 inch Macbook Pro, or the 12.9 inch iPad Pro, I usually choose the iPad. With Blink in full screen, it's basically the same as iTerm on the Macbook, but much more portable (and I can do things on the iPad I can't do on the Laptop: Apple Pencil & Goodnotes)