The compressor went bad on my '14 REX (72k miles) at the end of last year. It was still functional, but made a high-pitched whirring noise - not quite a howl, but more intrusive than the REX - when the AC kicked in, and had thrown out an error code from the main battery. The local exotic car shop I took it to - the i3 felt very downmarket surrounded by Lambos, Ferraris and Porsches! but they also handle BMWs - said there were no metal filings, although they changed out the filter/dryer as a matter of course. Total was $2600 for the compressor itself and ~$900 for labor and the filter. I seem to remember reading somewhere (here, probably) that the BEV doesn't have the same filter/dryer setup as the REX, which might make it more susceptible to shavings, but my memory often plays tricks on me these days
so I may be (probably am) wrong.