I use an ergodox as well and I still manage to use my regular keyboard just fine but it feels bad. After drinking the ergonomic kool-aid you notice how awkward normal keyboards can sometimes be.

That being said I've made a script that uses xmodmap and xcape to emulate some of the functionality of my ergodox layout. Obviously I can't physically modify the keyboard but I can remap control to caps lock, use xcape to make it send escape when used on its own (and use "space cadet shifts" to input parentheses), I also like to shuffle some keys to make them easier to reach (for instance I don't use Alt a lot but I use Super to control my WM, so I use xmodmap to swap them on regular keyboards).

This is a very good question and it did in fact occur to me when I was designing the keyboard layout. Partly due to this concern I stuck with a QWERTY layout for alphabetic characters, so I'd at least retain some familiarity with traditional keyboards. Besides that, I'm typing on my laptop right now and often plug in a traditional keyboard if I'm gaming, so I haven't found lack of familiarity with a traditional keyboard a problem.

I do have some lingering switching issues, notably I've put -/_ and +/= on the left side since there isn't room on the right, and `/~ are below left instead of above left.

It's annoying for the first hour, then the muscle memory kicks in. It seems to be slowly but surely sinking in, I expect at some point my fingers will just learn which is which.