why? wouldn't the screen be too small to make any sense of the info? maybe if you can switch between the dev tools and the site super fast, otherwise you have to view the site and the dev tools side by side on a small screen
Modal Dev Tools, that's actually really a good idea on phones (screen size isn't a problem on tablets and STBs).
I believe a horizontal swipe could show or close the tools. That way you can still select the element in the content window and look back at the source. Since non-developers might get bogged down with it I'd suggest it be option you tick on in settings.
Coding on things other than a computer gets a little easier when the tools exist :)
I've made quick pushes via web IDE on my phone while commuting. I doubt improved tooling would increase frequency, but it would certainly increase the complexity I'd be capable of and my confidence in not pushing janky brokenness.
