A physical ESC isn't that important because multiple presses are idempotent usually; there's only one dialog in the foreground of the active application (at least there should be) or you're only in one insert mode. I also don't see this being a big deal for key-combos. As long as it's available in apps that make use of it or Apple let's you enable it, and there's a way for you to learn where it is by touch, this shouldn't be that big of a deal.