This isn't something that could be caused by a mutation in a single nucleotide or a segment being deleted or inserted, the way normal mutations happen and get passed on. This would be an entirely different set of (mirrored) machinery composing (mirrored) structures from (mirrored) subunits.

Whatever caused life to begin in the first place would maybe be the right place to look to recreate this naturally. If life began again from step 0, but with the opposite chirality, it could then progress forward towards mirrored bacteria.

Because it's too much of a lift at once. To naturally get a mirror E-Coli you'd need a separate planet and billions of years and lots of luck.

It's a mostly-incompatible change to all the machinery all the way down.

because as it was never observed to date, it could be assumed it does not exists yet, as the the article makes it sounds like it's very artificial / constructed