I use a Kinesis and Dvorak. I have no trouble at all switching between the Kinesis and a macbook keyboard (which is also set to Dvorak) but I'd definately be slow to type English (back to normal person typing speed), and writong code in vim would be a nightmare if I was forced to use a random machine and not able to switch the layout.
Luckily, you can switch easily to Dvorak on most systems for the last couple of decades. Something that's less true once you start inventing your own layouts (though I think Colemak, Neo and Workman are decently suppprted).
Also, people who learned to touch type QWERTY suggest you can swap back even after learning a new layout. I never learned qwerty that well but return to standard nerd level of familiarity.
Luckily, you can switch easily to Dvorak on most systems for the last couple of decades. Something that's less true once you start inventing your own layouts (though I think Colemak, Neo and Workman are decently suppprted).
Also, people who learned to touch type QWERTY suggest you can swap back even after learning a new layout. I never learned qwerty that well but return to standard nerd level of familiarity.