I realise that airline flying and flight instruction are quite different - I used to be a flight instructor in the US and I found teaching quite rewarding, unfortunately I rather foolishly allowed my CFI ticket to expire! I certainly wouldn't want to step on anyone's toes; I'd actually rather assumed that as an MEP CRI requires 30 hours PIC, and an FI requires 200 hours IFR to teach instruments then most non-career FI's would stick with SEP, and that MEIR instructors would be harder to find.